diff --git a/fuzzers/baby_fuzzer_minimizing/src/main.rs b/fuzzers/baby_fuzzer_minimizing/src/main.rs
index c909e3e34b..4cec8054af 100644
--- a/fuzzers/baby_fuzzer_minimizing/src/main.rs
+++ b/fuzzers/baby_fuzzer_minimizing/src/main.rs
@@ -136,7 +136,13 @@ pub fn main() -> Result<(), Error> {
     let mut executor = InProcessExecutor::new(&mut harness, (), &mut fuzzer, &mut state, &mut mgr)?;
 
     state.load_initial_inputs_forced(&mut fuzzer, &mut executor, &mut mgr, &[solution_dir])?;
-    stages.perform_all(&mut fuzzer, &mut executor, &mut state, &mut mgr, 0)?;
+    stages.perform_all(
+        &mut fuzzer,
+        &mut executor,
+        &mut state,
+        &mut mgr,
+        CorpusId::from(0usize),
+    )?;
 
     Ok(())
 }
diff --git a/fuzzers/libfuzzer_libpng_launcher/src/lib.rs b/fuzzers/libfuzzer_libpng_launcher/src/lib.rs
index fc7d9daed9..b34e30789b 100644
--- a/fuzzers/libfuzzer_libpng_launcher/src/lib.rs
+++ b/fuzzers/libfuzzer_libpng_launcher/src/lib.rs
@@ -32,7 +32,7 @@ use libafl::{
         scheduled::{havoc_mutations, tokens_mutations, StdScheduledMutator},
         token_mutations::Tokens,
     },
-    observers::{HitcountsMapObserver, StdMapObserver, TimeObserver},
+    observers::{HitcountsMapObserver, TimeObserver},
     schedulers::{IndexesLenTimeMinimizerScheduler, QueueScheduler},
     stages::mutational::StdMutationalStage,
     state::{HasCorpus, HasMetadata, StdState},
diff --git a/libafl/Cargo.toml b/libafl/Cargo.toml
index eb8b465024..c6eaa1af5b 100644
--- a/libafl/Cargo.toml
+++ b/libafl/Cargo.toml
@@ -29,6 +29,7 @@ frida_cli = ["cli"]
 afl_exec_sec = [] # calculate exec/sec like AFL
 errors_backtrace = ["backtrace"]
 cmin = ["z3"] # corpus minimisation
+corpus_btreemap = []
 
 # features hiding dependencies licensed under GPL
 gpl = []
diff --git a/libafl/src/corpus/cached.rs b/libafl/src/corpus/cached.rs
index 51be87c462..135311ba5e 100644
--- a/libafl/src/corpus/cached.rs
+++ b/libafl/src/corpus/cached.rs
@@ -9,7 +9,7 @@ use serde::{Deserialize, Serialize};
 use crate::{
     corpus::{
         ondisk::{OnDiskCorpus, OnDiskMetadataFormat},
-        Corpus, Testcase,
+        Corpus, CorpusId, Testcase,
     },
     inputs::{Input, UsesInput},
     Error,
@@ -24,7 +24,7 @@ where
     I: Input,
 {
     inner: OnDiskCorpus<I>,
-    cached_indexes: RefCell<VecDeque<usize>>,
+    cached_indexes: RefCell<VecDeque<CorpusId>>,
     cache_max_len: usize,
 }
 
@@ -47,30 +47,28 @@ where
 
     /// Add an entry to the corpus and return its index
     #[inline]
-    fn add(&mut self, testcase: Testcase<I>) -> Result<usize, Error> {
+    fn add(&mut self, testcase: Testcase<I>) -> Result<CorpusId, Error> {
         self.inner.add(testcase)
     }
 
     /// Replaces the testcase at the given idx
     #[inline]
-    fn replace(&mut self, idx: usize, testcase: Testcase<I>) -> Result<Testcase<I>, Error> {
+    fn replace(&mut self, idx: CorpusId, testcase: Testcase<I>) -> Result<Testcase<I>, Error> {
         // TODO finish
         self.inner.replace(idx, testcase)
     }
 
     /// Removes an entry from the corpus, returning it if it was present.
     #[inline]
-    fn remove(&mut self, idx: usize) -> Result<Option<Testcase<I>>, Error> {
+    fn remove(&mut self, idx: CorpusId) -> Result<Testcase<I>, Error> {
         let testcase = self.inner.remove(idx)?;
-        if testcase.is_some() {
-            self.cached_indexes.borrow_mut().retain(|e| *e != idx);
-        }
+        self.cached_indexes.borrow_mut().retain(|e| *e != idx);
         Ok(testcase)
     }
 
     /// Get by id
     #[inline]
-    fn get(&self, idx: usize) -> Result<&RefCell<Testcase<I>>, Error> {
+    fn get(&self, idx: CorpusId) -> Result<&RefCell<Testcase<I>>, Error> {
         let testcase = { self.inner.get(idx)? };
         if testcase.borrow().input().is_none() {
             let _ = testcase.borrow_mut().load_input()?;
@@ -94,15 +92,40 @@ where
 
     /// Current testcase scheduled
     #[inline]
-    fn current(&self) -> &Option<usize> {
+    fn current(&self) -> &Option<CorpusId> {
         self.inner.current()
     }
 
     /// Current testcase scheduled (mutable)
     #[inline]
-    fn current_mut(&mut self) -> &mut Option<usize> {
+    fn current_mut(&mut self) -> &mut Option<CorpusId> {
         self.inner.current_mut()
     }
+
+    #[inline]
+    fn next(&self, idx: CorpusId) -> Option<CorpusId> {
+        self.inner.next(idx)
+    }
+
+    #[inline]
+    fn prev(&self, idx: CorpusId) -> Option<CorpusId> {
+        self.inner.prev(idx)
+    }
+
+    #[inline]
+    fn first(&self) -> Option<CorpusId> {
+        self.inner.first()
+    }
+
+    #[inline]
+    fn last(&self) -> Option<CorpusId> {
+        self.inner.last()
+    }
+
+    #[inline]
+    fn nth(&self, nth: usize) -> CorpusId {
+        self.inner.nth(nth)
+    }
 }
 
 impl<I> CachedOnDiskCorpus<I>
diff --git a/libafl/src/corpus/inmemory.rs b/libafl/src/corpus/inmemory.rs
index 0640274d9c..69093766d7 100644
--- a/libafl/src/corpus/inmemory.rs
+++ b/libafl/src/corpus/inmemory.rs
@@ -6,11 +6,284 @@ use core::cell::RefCell;
 use serde::{Deserialize, Serialize};
 
 use crate::{
-    corpus::{Corpus, Testcase},
+    corpus::{Corpus, CorpusId, Testcase},
     inputs::{Input, UsesInput},
     Error,
 };
 
+/// Keep track of the stored `Testcase` and the siblings ids (insertion order)
+#[cfg(not(feature = "corpus_btreemap"))]
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(bound = "I: serde::de::DeserializeOwned")]
+pub struct TestcaseStorageItem<I>
+where
+    I: Input,
+{
+    /// The stored testcase
+    pub testcase: RefCell<Testcase<I>>,
+    /// Previously inserted id
+    pub prev: Option<CorpusId>,
+    /// Following inserted id
+    pub next: Option<CorpusId>,
+}
+
+#[cfg(not(feature = "corpus_btreemap"))]
+/// The map type in which testcases are stored (enable the feature `corpus_btreemap` to use a `BTreeMap` instead of `HashMap`)
+pub type TestcaseStorageMap<I> = hashbrown::HashMap<CorpusId, TestcaseStorageItem<I>>;
+
+#[cfg(feature = "corpus_btreemap")]
+/// The map type in which testcases are stored (disable the feature `corpus_btreemap` to use a `HashMap` instead of `BTreeMap`)
+pub type TestcaseStorageMap<I> =
+    alloc::collections::btree_map::BTreeMap<CorpusId, RefCell<Testcase<I>>>;
+
+/// Storage map for the testcases (used in `Corpus` implementations) with an incremental index
+#[derive(Default, Serialize, Deserialize, Clone, Debug)]
+#[serde(bound = "I: serde::de::DeserializeOwned")]
+pub struct TestcaseStorage<I>
+where
+    I: Input,
+{
+    /// The map in which testcases are stored
+    pub map: TestcaseStorageMap<I>,
+    /// The keys in order (use `Vec::binary_search`)
+    pub keys: Vec<CorpusId>,
+    /// The progressive idx
+    progressive_idx: usize,
+    /// First inserted idx
+    #[cfg(not(feature = "corpus_btreemap"))]
+    first_idx: Option<CorpusId>,
+    /// Last inserted idx
+    #[cfg(not(feature = "corpus_btreemap"))]
+    last_idx: Option<CorpusId>,
+}
+
+impl<I> UsesInput for TestcaseStorage<I>
+where
+    I: Input,
+{
+    type Input = I;
+}
+
+impl<I> TestcaseStorage<I>
+where
+    I: Input,
+{
+    /// Insert a key in the keys set
+    fn insert_key(&mut self, id: CorpusId) {
+        if let Err(idx) = self.keys.binary_search(&id) {
+            self.keys.insert(idx, id);
+        }
+    }
+
+    /// Remove a key from the keys set
+    fn remove_key(&mut self, id: CorpusId) {
+        if let Ok(idx) = self.keys.binary_search(&id) {
+            self.keys.remove(idx);
+        }
+    }
+
+    /// Insert a testcase assigning a `CorpusId` to it
+    #[cfg(not(feature = "corpus_btreemap"))]
+    pub fn insert(&mut self, testcase: RefCell<Testcase<I>>) -> CorpusId {
+        let idx = CorpusId::from(self.progressive_idx);
+        self.progressive_idx += 1;
+        let prev = if let Some(last_idx) = self.last_idx {
+            self.map.get_mut(&last_idx).unwrap().next = Some(idx);
+            Some(last_idx)
+        } else {
+            None
+        };
+        if self.first_idx.is_none() {
+            self.first_idx = Some(idx);
+        }
+        self.last_idx = Some(idx);
+        self.insert_key(idx);
+        self.map.insert(
+            idx,
+            TestcaseStorageItem {
+                testcase,
+                prev,
+                next: None,
+            },
+        );
+        idx
+    }
+
+    /// Insert a testcase assigning a `CorpusId` to it
+    #[cfg(feature = "corpus_btreemap")]
+    pub fn insert(&mut self, testcase: RefCell<Testcase<I>>) -> CorpusId {
+        let idx = CorpusId::from(self.progressive_idx);
+        self.progressive_idx += 1;
+        self.insert_key(idx);
+        self.map.insert(idx, testcase);
+        idx
+    }
+
+    /// Replace a testcase given a `CorpusId`
+    #[cfg(not(feature = "corpus_btreemap"))]
+    pub fn replace(&mut self, idx: CorpusId, testcase: Testcase<I>) -> Option<Testcase<I>> {
+        if let Some(entry) = self.map.get_mut(&idx) {
+            Some(entry.testcase.replace(testcase))
+        } else {
+            None
+        }
+    }
+
+    /// Replace a testcase given a `CorpusId`
+    #[cfg(feature = "corpus_btreemap")]
+    pub fn replace(&mut self, idx: CorpusId, testcase: Testcase<I>) -> Option<Testcase<I>> {
+        self.map.get_mut(&idx).map(|entry| entry.replace(testcase))
+    }
+
+    /// Remove a testcase given a `CorpusId`
+    #[cfg(not(feature = "corpus_btreemap"))]
+    pub fn remove(&mut self, idx: CorpusId) -> Option<RefCell<Testcase<I>>> {
+        if let Some(item) = self.map.remove(&idx) {
+            self.remove_key(idx);
+            if let Some(prev) = item.prev {
+                self.map.get_mut(&prev).unwrap().next = item.next;
+            } else {
+                // first elem
+                self.first_idx = item.next;
+            }
+            if let Some(next) = item.next {
+                self.map.get_mut(&next).unwrap().prev = item.prev;
+            } else {
+                // last elem
+                self.last_idx = item.prev;
+            }
+            Some(item.testcase)
+        } else {
+            None
+        }
+    }
+
+    /// Remove a testcase given a `CorpusId`
+    #[cfg(feature = "corpus_btreemap")]
+    pub fn remove(&mut self, idx: CorpusId) -> Option<RefCell<Testcase<I>>> {
+        self.remove_key(idx);
+        self.map.remove(&idx)
+    }
+
+    /// Get a testcase given a `CorpusId`
+    #[cfg(not(feature = "corpus_btreemap"))]
+    #[must_use]
+    pub fn get(&self, idx: CorpusId) -> Option<&RefCell<Testcase<I>>> {
+        self.map.get(&idx).as_ref().map(|x| &x.testcase)
+    }
+
+    /// Get a testcase given a `CorpusId`
+    #[cfg(feature = "corpus_btreemap")]
+    #[must_use]
+    pub fn get(&self, idx: CorpusId) -> Option<&RefCell<Testcase<I>>> {
+        self.map.get(&idx)
+    }
+
+    /// Get the next id given a `CorpusId` (creation order)
+    #[cfg(not(feature = "corpus_btreemap"))]
+    #[must_use]
+    fn next(&self, idx: CorpusId) -> Option<CorpusId> {
+        if let Some(item) = self.map.get(&idx) {
+            item.next
+        } else {
+            None
+        }
+    }
+
+    /// Get the next id given a `CorpusId` (creation order)
+    #[cfg(feature = "corpus_btreemap")]
+    #[must_use]
+    fn next(&self, idx: CorpusId) -> Option<CorpusId> {
+        // TODO see if using self.keys is faster
+        let mut range = self
+            .map
+            .range((core::ops::Bound::Included(idx), core::ops::Bound::Unbounded));
+        if let Some((this_id, _)) = range.next() {
+            if idx != *this_id {
+                return None;
+            }
+        }
+        if let Some((next_id, _)) = range.next() {
+            Some(*next_id)
+        } else {
+            None
+        }
+    }
+
+    /// Get the previous id given a `CorpusId` (creation order)
+    #[cfg(not(feature = "corpus_btreemap"))]
+    #[must_use]
+    fn prev(&self, idx: CorpusId) -> Option<CorpusId> {
+        if let Some(item) = self.map.get(&idx) {
+            item.prev
+        } else {
+            None
+        }
+    }
+
+    /// Get the previous id given a `CorpusId` (creation order)
+    #[cfg(feature = "corpus_btreemap")]
+    #[must_use]
+    fn prev(&self, idx: CorpusId) -> Option<CorpusId> {
+        // TODO see if using self.keys is faster
+        let mut range = self
+            .map
+            .range((core::ops::Bound::Unbounded, core::ops::Bound::Included(idx)));
+        if let Some((this_id, _)) = range.next_back() {
+            if idx != *this_id {
+                return None;
+            }
+        }
+        if let Some((prev_id, _)) = range.next_back() {
+            Some(*prev_id)
+        } else {
+            None
+        }
+    }
+
+    /// Get the first created id
+    #[cfg(not(feature = "corpus_btreemap"))]
+    #[must_use]
+    fn first(&self) -> Option<CorpusId> {
+        self.first_idx
+    }
+
+    /// Get the first created id
+    #[cfg(feature = "corpus_btreemap")]
+    #[must_use]
+    fn first(&self) -> Option<CorpusId> {
+        self.map.iter().next().map(|x| *x.0)
+    }
+
+    /// Get the last created id
+    #[cfg(not(feature = "corpus_btreemap"))]
+    #[must_use]
+    fn last(&self) -> Option<CorpusId> {
+        self.last_idx
+    }
+
+    /// Get the last created id
+    #[cfg(feature = "corpus_btreemap")]
+    #[must_use]
+    fn last(&self) -> Option<CorpusId> {
+        self.map.iter().next_back().map(|x| *x.0)
+    }
+
+    /// Create new `TestcaseStorage`
+    #[must_use]
+    pub fn new() -> Self {
+        Self {
+            map: TestcaseStorageMap::default(),
+            keys: vec![],
+            progressive_idx: 0,
+            #[cfg(not(feature = "corpus_btreemap"))]
+            first_idx: None,
+            #[cfg(not(feature = "corpus_btreemap"))]
+            last_idx: None,
+        }
+    }
+}
+
 /// A corpus handling all in memory.
 #[derive(Default, Serialize, Deserialize, Clone, Debug)]
 #[serde(bound = "I: serde::de::DeserializeOwned")]
@@ -18,8 +291,8 @@ pub struct InMemoryCorpus<I>
 where
     I: Input,
 {
-    entries: Vec<RefCell<Testcase<I>>>,
-    current: Option<usize>,
+    storage: TestcaseStorage<I>,
+    current: Option<CorpusId>,
 }
 
 impl<I> UsesInput for InMemoryCorpus<I>
@@ -36,52 +309,76 @@ where
     /// Returns the number of elements
     #[inline]
     fn count(&self) -> usize {
-        self.entries.len()
+        self.storage.map.len()
     }
 
     /// Add an entry to the corpus and return its index
     #[inline]
-    fn add(&mut self, testcase: Testcase<I>) -> Result<usize, Error> {
-        self.entries.push(RefCell::new(testcase));
-        Ok(self.entries.len() - 1)
+    fn add(&mut self, testcase: Testcase<I>) -> Result<CorpusId, Error> {
+        Ok(self.storage.insert(RefCell::new(testcase)))
     }
 
     /// Replaces the testcase at the given idx
     #[inline]
-    fn replace(&mut self, idx: usize, testcase: Testcase<I>) -> Result<Testcase<I>, Error> {
-        if idx >= self.entries.len() {
-            return Err(Error::key_not_found(format!("Index {idx} out of bounds")));
-        }
-        Ok(self.entries[idx].replace(testcase))
+    fn replace(&mut self, idx: CorpusId, testcase: Testcase<I>) -> Result<Testcase<I>, Error> {
+        self.storage
+            .replace(idx, testcase)
+            .ok_or_else(|| Error::key_not_found(format!("Index {idx} not found")))
     }
 
     /// Removes an entry from the corpus, returning it if it was present.
     #[inline]
-    fn remove(&mut self, idx: usize) -> Result<Option<Testcase<I>>, Error> {
-        if idx >= self.entries.len() {
-            Ok(None)
-        } else {
-            Ok(Some(self.entries.remove(idx).into_inner()))
-        }
+    fn remove(&mut self, idx: CorpusId) -> Result<Testcase<I>, Error> {
+        self.storage
+            .remove(idx)
+            .map(|x| x.take())
+            .ok_or_else(|| Error::key_not_found(format!("Index {idx} not found")))
     }
 
     /// Get by id
     #[inline]
-    fn get(&self, idx: usize) -> Result<&RefCell<Testcase<I>>, Error> {
-        Ok(&self.entries[idx])
+    fn get(&self, idx: CorpusId) -> Result<&RefCell<Testcase<I>>, Error> {
+        self.storage
+            .get(idx)
+            .ok_or_else(|| Error::key_not_found(format!("Index {idx} not found")))
     }
 
     /// Current testcase scheduled
     #[inline]
-    fn current(&self) -> &Option<usize> {
+    fn current(&self) -> &Option<CorpusId> {
         &self.current
     }
 
     /// Current testcase scheduled (mutable)
     #[inline]
-    fn current_mut(&mut self) -> &mut Option<usize> {
+    fn current_mut(&mut self) -> &mut Option<CorpusId> {
         &mut self.current
     }
+
+    #[inline]
+    fn next(&self, idx: CorpusId) -> Option<CorpusId> {
+        self.storage.next(idx)
+    }
+
+    #[inline]
+    fn prev(&self, idx: CorpusId) -> Option<CorpusId> {
+        self.storage.prev(idx)
+    }
+
+    #[inline]
+    fn first(&self) -> Option<CorpusId> {
+        self.storage.first()
+    }
+
+    #[inline]
+    fn last(&self) -> Option<CorpusId> {
+        self.storage.last()
+    }
+
+    #[inline]
+    fn nth(&self, nth: usize) -> CorpusId {
+        self.storage.keys[nth]
+    }
 }
 
 impl<I> InMemoryCorpus<I>
@@ -93,7 +390,7 @@ where
     #[must_use]
     pub fn new() -> Self {
         Self {
-            entries: vec![],
+            storage: TestcaseStorage::new(),
             current: None,
         }
     }
diff --git a/libafl/src/corpus/minimizer.rs b/libafl/src/corpus/minimizer.rs
index 577dea31bd..a0063e4946 100644
--- a/libafl/src/corpus/minimizer.rs
+++ b/libafl/src/corpus/minimizer.rs
@@ -111,7 +111,8 @@ where
         let mut seed_exprs = HashMap::new();
         let mut cov_map = HashMap::new();
 
-        for idx in 0..state.corpus().count() {
+        let mut cur_id = state.corpus().first();
+        while let Some(idx) = cur_id {
             let (weight, input) = {
                 let mut testcase = state.corpus().get(idx)?.borrow_mut();
                 let weight = TS::compute(&mut *testcase, state)?
@@ -151,6 +152,8 @@ where
 
             // Keep track of that seed's index and weight
             seed_exprs.insert(seed_expr, (idx, weight));
+
+            cur_id = state.corpus().next(idx);
         }
 
         for (_, cov) in cov_map {
@@ -191,7 +194,9 @@ where
                 let removed = state.corpus_mut().remove(idx)?;
                 // scheduler needs to know we've removed the input, or it will continue to try
                 // to use now-missing inputs
-                fuzzer.scheduler_mut().on_remove(state, idx, &removed)?;
+                fuzzer
+                    .scheduler_mut()
+                    .on_remove(state, idx, &Some(removed))?;
             }
             Ok(())
         } else {
diff --git a/libafl/src/corpus/mod.rs b/libafl/src/corpus/mod.rs
index dadbec6953..4116128e5e 100644
--- a/libafl/src/corpus/mod.rs
+++ b/libafl/src/corpus/mod.rs
@@ -18,15 +18,49 @@ pub use cached::CachedOnDiskCorpus;
 
 #[cfg(feature = "cmin")]
 pub mod minimizer;
-use core::cell::RefCell;
+use core::{cell::RefCell, fmt};
 
 #[cfg(feature = "cmin")]
 pub use minimizer::*;
+use serde::{Deserialize, Serialize};
 
 use crate::{inputs::UsesInput, Error};
 
+/// An abstraction for the index that identify a testcase in the corpus
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Serialize, Deserialize)]
+#[repr(transparent)]
+pub struct CorpusId(pub(crate) usize);
+
+impl fmt::Display for CorpusId {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+impl From<usize> for CorpusId {
+    fn from(id: usize) -> Self {
+        Self(id)
+    }
+}
+
+impl From<u64> for CorpusId {
+    fn from(id: u64) -> Self {
+        Self(id as usize)
+    }
+}
+
+/// Utility macro to call `Corpus::random_id`
+#[macro_export]
+macro_rules! random_corpus_id {
+    ($corpus:expr, $rand:expr) => {{
+        let cnt = $corpus.count() as u64;
+        let nth = $rand.below(cnt) as usize;
+        $corpus.nth(nth)
+    }};
+}
+
 /// Corpus with all current testcases
-pub trait Corpus: UsesInput + serde::Serialize + for<'de> serde::Deserialize<'de> {
+pub trait Corpus: UsesInput + Serialize + for<'de> Deserialize<'de> {
     /// Returns the number of elements
     fn count(&self) -> usize;
 
@@ -36,26 +70,95 @@ pub trait Corpus: UsesInput + serde::Serialize + for<'de> serde::Deserialize<'de
     }
 
     /// Add an entry to the corpus and return its index
-    fn add(&mut self, testcase: Testcase<Self::Input>) -> Result<usize, Error>;
+    fn add(&mut self, testcase: Testcase<Self::Input>) -> Result<CorpusId, Error>;
 
     /// Replaces the testcase at the given idx, returning the existing.
     fn replace(
         &mut self,
-        idx: usize,
+        idx: CorpusId,
         testcase: Testcase<Self::Input>,
     ) -> Result<Testcase<Self::Input>, Error>;
 
     /// Removes an entry from the corpus, returning it if it was present.
-    fn remove(&mut self, idx: usize) -> Result<Option<Testcase<Self::Input>>, Error>;
+    fn remove(&mut self, id: CorpusId) -> Result<Testcase<Self::Input>, Error>;
 
     /// Get by id
-    fn get(&self, idx: usize) -> Result<&RefCell<Testcase<Self::Input>>, Error>;
+    fn get(&self, id: CorpusId) -> Result<&RefCell<Testcase<Self::Input>>, Error>;
 
     /// Current testcase scheduled
-    fn current(&self) -> &Option<usize>;
+    fn current(&self) -> &Option<CorpusId>;
 
     /// Current testcase scheduled (mutable)
-    fn current_mut(&mut self) -> &mut Option<usize>;
+    fn current_mut(&mut self) -> &mut Option<CorpusId>;
+
+    /// Get the next corpus id
+    fn next(&self, id: CorpusId) -> Option<CorpusId>;
+
+    /// Get the prev corpus id
+    fn prev(&self, id: CorpusId) -> Option<CorpusId>;
+
+    /// Get the first inserted corpus id
+    fn first(&self) -> Option<CorpusId>;
+
+    /// Get the last inserted corpus id
+    fn last(&self) -> Option<CorpusId>;
+
+    /// An iterator over very active corpus id
+    fn ids(&self) -> CorpusIdIterator<'_, Self> {
+        CorpusIdIterator {
+            corpus: self,
+            cur: self.first(),
+            cur_back: self.last(),
+        }
+    }
+
+    /// Get the nth corpus id
+    fn nth(&self, nth: usize) -> CorpusId {
+        self.ids()
+            .nth(nth)
+            .expect("Failed to get the {nth} CorpusId")
+    }
+}
+
+/// `Iterator` over the ids of a `Corpus`
+#[derive(Debug)]
+pub struct CorpusIdIterator<'a, C>
+where
+    C: Corpus,
+{
+    corpus: &'a C,
+    cur: Option<CorpusId>,
+    cur_back: Option<CorpusId>,
+}
+
+impl<'a, C> Iterator for CorpusIdIterator<'a, C>
+where
+    C: Corpus,
+{
+    type Item = CorpusId;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Some(cur) = self.cur {
+            self.cur = self.corpus.next(cur);
+            Some(cur)
+        } else {
+            None
+        }
+    }
+}
+
+impl<'a, C> DoubleEndedIterator for CorpusIdIterator<'a, C>
+where
+    C: Corpus,
+{
+    fn next_back(&mut self) -> Option<Self::Item> {
+        if let Some(cur_back) = self.cur_back {
+            self.cur_back = self.corpus.prev(cur_back);
+            Some(cur_back)
+        } else {
+            None
+        }
+    }
 }
 
 /// `Corpus` Python bindings
@@ -71,7 +174,7 @@ pub mod pybind {
         corpus::{
             cached::pybind::PythonCachedOnDiskCorpus, inmemory::pybind::PythonInMemoryCorpus,
             ondisk::pybind::PythonOnDiskCorpus, testcase::pybind::PythonTestcaseWrapper, Corpus,
-            Testcase,
+            CorpusId, Testcase,
         },
         inputs::{BytesInput, UsesInput},
         Error,
@@ -157,13 +260,13 @@ pub mod pybind {
 
         #[pyo3(name = "current")]
         fn pycurrent(&self) -> Option<usize> {
-            *self.current()
+            self.current().map(|x| x.0)
         }
 
         #[pyo3(name = "get")]
         fn pyget(&self, idx: usize) -> PythonTestcaseWrapper {
             let t: &mut Testcase<BytesInput> = unwrap_me!(self.wrapper, c, {
-                c.get(idx)
+                c.get(CorpusId::from(idx))
                     .map(|v| unsafe { v.as_ptr().as_mut().unwrap() })
                     .expect("PythonCorpus::get failed")
             });
@@ -182,26 +285,26 @@ pub mod pybind {
         }
 
         #[inline]
-        fn add(&mut self, testcase: Testcase<BytesInput>) -> Result<usize, Error> {
+        fn add(&mut self, testcase: Testcase<BytesInput>) -> Result<CorpusId, Error> {
             unwrap_me_mut!(self.wrapper, c, { c.add(testcase) })
         }
 
         #[inline]
         fn replace(
             &mut self,
-            idx: usize,
+            idx: CorpusId,
             testcase: Testcase<BytesInput>,
         ) -> Result<Testcase<BytesInput>, Error> {
             unwrap_me_mut!(self.wrapper, c, { c.replace(idx, testcase) })
         }
 
         #[inline]
-        fn remove(&mut self, idx: usize) -> Result<Option<Testcase<BytesInput>>, Error> {
+        fn remove(&mut self, idx: CorpusId) -> Result<Testcase<BytesInput>, Error> {
             unwrap_me_mut!(self.wrapper, c, { c.remove(idx) })
         }
 
         #[inline]
-        fn get(&self, idx: usize) -> Result<&RefCell<Testcase<BytesInput>>, Error> {
+        fn get(&self, idx: CorpusId) -> Result<&RefCell<Testcase<BytesInput>>, Error> {
             let ptr = unwrap_me!(self.wrapper, c, {
                 c.get(idx)
                     .map(|v| v as *const RefCell<Testcase<BytesInput>>)
@@ -210,16 +313,49 @@ pub mod pybind {
         }
 
         #[inline]
-        fn current(&self) -> &Option<usize> {
-            let ptr = unwrap_me!(self.wrapper, c, { c.current() as *const Option<usize> });
+        fn current(&self) -> &Option<CorpusId> {
+            let ptr = unwrap_me!(self.wrapper, c, { c.current() as *const Option<CorpusId> });
             unsafe { ptr.as_ref().unwrap() }
         }
 
         #[inline]
-        fn current_mut(&mut self) -> &mut Option<usize> {
-            let ptr = unwrap_me_mut!(self.wrapper, c, { c.current_mut() as *mut Option<usize> });
+        fn current_mut(&mut self) -> &mut Option<CorpusId> {
+            let ptr = unwrap_me_mut!(self.wrapper, c, {
+                c.current_mut() as *mut Option<CorpusId>
+            });
             unsafe { ptr.as_mut().unwrap() }
         }
+
+        fn next(&self, idx: CorpusId) -> Option<CorpusId> {
+            unwrap_me!(self.wrapper, c, { c.next(idx) })
+        }
+
+        fn prev(&self, idx: CorpusId) -> Option<CorpusId> {
+            unwrap_me!(self.wrapper, c, { c.prev(idx) })
+        }
+
+        fn first(&self) -> Option<CorpusId> {
+            unwrap_me!(self.wrapper, c, { c.first() })
+        }
+
+        fn last(&self) -> Option<CorpusId> {
+            unwrap_me!(self.wrapper, c, { c.last() })
+        }
+
+        /*fn ids<'a>(&'a self) -> CorpusIdIterator<'a, Self> {
+            CorpusIdIterator {
+                corpus: self,
+                cur: self.first(),
+                cur_back: self.last(),
+            }
+        }
+
+        fn random_id(&self, next_random: u64) -> CorpusId {
+            let nth = (next_random as usize) % self.count();
+            self.ids()
+                .nth(nth)
+                .expect("Failed to get a random CorpusId")
+        }*/
     }
 
     /// Register the classes to the python module
diff --git a/libafl/src/corpus/ondisk.rs b/libafl/src/corpus/ondisk.rs
index bc031e1aaa..6712ce858d 100644
--- a/libafl/src/corpus/ondisk.rs
+++ b/libafl/src/corpus/ondisk.rs
@@ -1,6 +1,5 @@
 //! The ondisk corpus stores unused testcases to disk.
 
-use alloc::vec::Vec;
 use core::{cell::RefCell, time::Duration};
 #[cfg(feature = "std")]
 use std::{fs, fs::File, io::Write};
@@ -13,7 +12,7 @@ use serde::{Deserialize, Serialize};
 
 use crate::{
     bolts::serdeany::SerdeAnyMap,
-    corpus::{Corpus, Testcase},
+    corpus::{Corpus, CorpusId, InMemoryCorpus, Testcase},
     inputs::{Input, UsesInput},
     state::HasMetadata,
     Error,
@@ -48,8 +47,7 @@ pub struct OnDiskCorpus<I>
 where
     I: Input,
 {
-    entries: Vec<RefCell<Testcase<I>>>,
-    current: Option<usize>,
+    inner: InMemoryCorpus<I>,
     dir_path: PathBuf,
     meta_format: Option<OnDiskMetadataFormat>,
 }
@@ -68,57 +66,75 @@ where
     /// Returns the number of elements
     #[inline]
     fn count(&self) -> usize {
-        self.entries.len()
+        self.inner.count()
     }
 
     /// Add an entry to the corpus and return its index
     #[inline]
-    fn add(&mut self, mut testcase: Testcase<I>) -> Result<usize, Error> {
-        self.save_testcase(&mut testcase)?;
-        self.entries.push(RefCell::new(testcase));
-        Ok(self.entries.len() - 1)
+    fn add(&mut self, testcase: Testcase<I>) -> Result<CorpusId, Error> {
+        let idx = self.inner.add(testcase)?;
+        self.save_testcase(&mut self.get(idx).unwrap().borrow_mut(), idx)?;
+        Ok(idx)
     }
 
     /// Replaces the testcase at the given idx
     #[inline]
-    fn replace(&mut self, idx: usize, mut testcase: Testcase<I>) -> Result<Testcase<I>, Error> {
-        if idx >= self.entries.len() {
-            return Err(Error::key_not_found(format!("Index {idx} out of bounds")));
-        }
-        self.save_testcase(&mut testcase)?;
-        let previous = self.entries[idx].replace(testcase);
-        self.remove_testcase(&previous)?;
-        Ok(previous)
+    fn replace(&mut self, idx: CorpusId, testcase: Testcase<I>) -> Result<Testcase<I>, Error> {
+        let entry = self.inner.replace(idx, testcase)?;
+        self.remove_testcase(&entry)?;
+        self.save_testcase(&mut self.get(idx).unwrap().borrow_mut(), idx)?;
+        Ok(entry)
     }
 
     /// Removes an entry from the corpus, returning it if it was present.
     #[inline]
-    fn remove(&mut self, idx: usize) -> Result<Option<Testcase<I>>, Error> {
-        if idx >= self.entries.len() {
-            Ok(None)
-        } else {
-            let prev = self.entries.remove(idx).into_inner();
-            self.remove_testcase(&prev)?;
-            Ok(Some(prev))
-        }
+    fn remove(&mut self, idx: CorpusId) -> Result<Testcase<I>, Error> {
+        let entry = self.inner.remove(idx)?;
+        self.remove_testcase(&entry)?;
+        Ok(entry)
     }
 
     /// Get by id
     #[inline]
-    fn get(&self, idx: usize) -> Result<&RefCell<Testcase<I>>, Error> {
-        Ok(&self.entries[idx])
+    fn get(&self, idx: CorpusId) -> Result<&RefCell<Testcase<I>>, Error> {
+        self.inner.get(idx)
     }
 
     /// Current testcase scheduled
     #[inline]
-    fn current(&self) -> &Option<usize> {
-        &self.current
+    fn current(&self) -> &Option<CorpusId> {
+        self.inner.current()
     }
 
     /// Current testcase scheduled (mutable)
     #[inline]
-    fn current_mut(&mut self) -> &mut Option<usize> {
-        &mut self.current
+    fn current_mut(&mut self) -> &mut Option<CorpusId> {
+        self.inner.current_mut()
+    }
+
+    #[inline]
+    fn next(&self, idx: CorpusId) -> Option<CorpusId> {
+        self.inner.next(idx)
+    }
+
+    #[inline]
+    fn prev(&self, idx: CorpusId) -> Option<CorpusId> {
+        self.inner.prev(idx)
+    }
+
+    #[inline]
+    fn first(&self) -> Option<CorpusId> {
+        self.inner.first()
+    }
+
+    #[inline]
+    fn last(&self) -> Option<CorpusId> {
+        self.inner.last()
+    }
+
+    #[inline]
+    fn nth(&self, nth: usize) -> CorpusId {
+        self.inner.nth(nth)
     }
 }
 
@@ -135,8 +151,7 @@ where
         fn new<I: Input>(dir_path: PathBuf) -> Result<OnDiskCorpus<I>, Error> {
             fs::create_dir_all(&dir_path)?;
             Ok(OnDiskCorpus {
-                entries: vec![],
-                current: None,
+                inner: InMemoryCorpus::new(),
                 dir_path,
                 meta_format: None,
             })
@@ -152,21 +167,16 @@ where
     ) -> Result<Self, Error> {
         fs::create_dir_all(&dir_path)?;
         Ok(Self {
-            entries: vec![],
-            current: None,
+            inner: InMemoryCorpus::new(),
             dir_path,
             meta_format,
         })
     }
 
-    fn save_testcase(&mut self, testcase: &mut Testcase<I>) -> Result<(), Error> {
+    fn save_testcase(&self, testcase: &mut Testcase<I>, idx: CorpusId) -> Result<(), Error> {
         if testcase.filename().is_none() {
             // TODO walk entry metadata to ask for pieces of filename (e.g. :havoc in AFL)
-            let file_orig = testcase
-                .input()
-                .as_ref()
-                .unwrap()
-                .generate_name(self.entries.len());
+            let file_orig = testcase.input().as_ref().unwrap().generate_name(idx.0);
             let mut file = file_orig.clone();
 
             let mut ctr = 2;
@@ -224,7 +234,7 @@ where
         Ok(())
     }
 
-    fn remove_testcase(&mut self, testcase: &Testcase<I>) -> Result<(), Error> {
+    fn remove_testcase(&self, testcase: &Testcase<I>) -> Result<(), Error> {
         if let Some(filename) = testcase.filename() {
             fs::remove_file(filename)?;
         }
diff --git a/libafl/src/fuzzer/mod.rs b/libafl/src/fuzzer/mod.rs
index 7784bf8604..c5a59d106c 100644
--- a/libafl/src/fuzzer/mod.rs
+++ b/libafl/src/fuzzer/mod.rs
@@ -13,7 +13,7 @@ use crate::monitors::PerfFeature;
 use crate::state::NopState;
 use crate::{
     bolts::current_time,
-    corpus::{Corpus, Testcase},
+    corpus::{Corpus, CorpusId, Testcase},
     events::{Event, EventConfig, EventFirer, EventProcessor, ProgressReporter},
     executors::{Executor, ExitKind, HasObservers},
     feedbacks::Feedback,
@@ -83,7 +83,7 @@ pub trait ExecutionProcessor<OT>: UsesState {
         observers: &OT,
         exit_kind: &ExitKind,
         send_events: bool,
-    ) -> Result<(ExecuteInputResult, Option<usize>), Error>
+    ) -> Result<(ExecuteInputResult, Option<CorpusId>), Error>
     where
         EM: EventFirer<State = Self::State>;
 }
@@ -100,7 +100,7 @@ pub trait EvaluatorObservers<OT>: UsesState + Sized {
         manager: &mut EM,
         input: <Self::State as UsesInput>::Input,
         send_events: bool,
-    ) -> Result<(ExecuteInputResult, Option<usize>), Error>
+    ) -> Result<(ExecuteInputResult, Option<CorpusId>), Error>
     where
         E: Executor<EM, Self> + HasObservers<Observers = OT, State = Self::State>,
         EM: EventFirer<State = Self::State>;
@@ -120,7 +120,7 @@ where
         executor: &mut E,
         manager: &mut EM,
         input: <Self::State as UsesInput>::Input,
-    ) -> Result<(ExecuteInputResult, Option<usize>), Error> {
+    ) -> Result<(ExecuteInputResult, Option<CorpusId>), Error> {
         self.evaluate_input_events(state, executor, manager, input, true)
     }
 
@@ -134,7 +134,7 @@ where
         manager: &mut EM,
         input: <Self::State as UsesInput>::Input,
         send_events: bool,
-    ) -> Result<(ExecuteInputResult, Option<usize>), Error>;
+    ) -> Result<(ExecuteInputResult, Option<CorpusId>), Error>;
 
     /// Runs the input and triggers observers and feedback.
     /// Adds an input, to the corpus even if it's not considered `interesting` by the `feedback`.
@@ -146,7 +146,7 @@ where
         executor: &mut E,
         manager: &mut EM,
         input: <Self::State as UsesInput>::Input,
-    ) -> Result<usize, Error>;
+    ) -> Result<CorpusId, Error>;
 }
 
 /// The main fuzzer trait.
@@ -172,7 +172,7 @@ where
         executor: &mut E,
         state: &mut EM::State,
         manager: &mut EM,
-    ) -> Result<usize, Error>;
+    ) -> Result<CorpusId, Error>;
 
     /// Fuzz forever (or until stopped)
     fn fuzz_loop(
@@ -181,7 +181,7 @@ where
         executor: &mut E,
         state: &mut EM::State,
         manager: &mut EM,
-    ) -> Result<usize, Error> {
+    ) -> Result<CorpusId, Error> {
         let mut last = current_time();
         let monitor_timeout = STATS_TIMEOUT_DEFAULT;
         loop {
@@ -206,19 +206,19 @@ where
         state: &mut EM::State,
         manager: &mut EM,
         iters: u64,
-    ) -> Result<usize, Error> {
+    ) -> Result<CorpusId, Error> {
         if iters == 0 {
             return Err(Error::illegal_argument(
                 "Cannot fuzz for 0 iterations!".to_string(),
             ));
         }
 
-        let mut ret = 0;
+        let mut ret = None;
         let mut last = current_time();
         let monitor_timeout = STATS_TIMEOUT_DEFAULT;
 
         for _ in 0..iters {
-            ret = self.fuzz_one(stages, executor, state, manager)?;
+            ret = Some(self.fuzz_one(stages, executor, state, manager)?);
             last = manager.maybe_report_progress(state, last, monitor_timeout)?;
         }
 
@@ -227,7 +227,7 @@ where
         // But as the state may grow to a few megabytes,
         // for now we won' and the user has to do it (unless we find a way to do this on `Drop`).
 
-        Ok(ret)
+        Ok(ret.unwrap())
     }
 }
 
@@ -338,7 +338,7 @@ where
         observers: &OT,
         exit_kind: &ExitKind,
         send_events: bool,
-    ) -> Result<(ExecuteInputResult, Option<usize>), Error>
+    ) -> Result<(ExecuteInputResult, Option<CorpusId>), Error>
     where
         EM: EventFirer<State = Self::State>,
     {
@@ -451,7 +451,7 @@ where
         manager: &mut EM,
         input: <Self::State as UsesInput>::Input,
         send_events: bool,
-    ) -> Result<(ExecuteInputResult, Option<usize>), Error>
+    ) -> Result<(ExecuteInputResult, Option<CorpusId>), Error>
     where
         E: Executor<EM, Self> + HasObservers<Observers = OT, State = Self::State>,
         EM: EventFirer<State = Self::State>,
@@ -481,7 +481,7 @@ where
         manager: &mut EM,
         input: <CS::State as UsesInput>::Input,
         send_events: bool,
-    ) -> Result<(ExecuteInputResult, Option<usize>), Error> {
+    ) -> Result<(ExecuteInputResult, Option<CorpusId>), Error> {
         self.evaluate_input_with_observers(state, executor, manager, input, send_events)
     }
 
@@ -492,7 +492,7 @@ where
         executor: &mut E,
         manager: &mut EM,
         input: <CS::State as UsesInput>::Input,
-    ) -> Result<usize, Error> {
+    ) -> Result<CorpusId, Error> {
         let exit_kind = self.execute_input(state, executor, manager, &input)?;
         let observers = executor.observers();
         // Always consider this to be "interesting"
@@ -543,7 +543,7 @@ where
         executor: &mut E,
         state: &mut CS::State,
         manager: &mut EM,
-    ) -> Result<usize, Error> {
+    ) -> Result<CorpusId, Error> {
         // Init timer for scheduler
         #[cfg(feature = "introspection")]
         state.introspection_monitor_mut().start_timer();
@@ -717,7 +717,7 @@ where
         _executor: &mut E,
         _state: &mut EM::State,
         _manager: &mut EM,
-    ) -> Result<usize, Error> {
+    ) -> Result<CorpusId, Error> {
         unimplemented!()
     }
 }
@@ -805,6 +805,7 @@ pub mod pybind {
                     BytesInput::new(input),
                 )
                 .expect("Failed to add input")
+                .0
         }
 
         fn fuzz_loop(
diff --git a/libafl/src/mutators/encoded_mutations.rs b/libafl/src/mutators/encoded_mutations.rs
index 74429ae5f7..9273ae38d8 100644
--- a/libafl/src/mutators/encoded_mutations.rs
+++ b/libafl/src/mutators/encoded_mutations.rs
@@ -14,6 +14,7 @@ use crate::{
         mutations::{buffer_copy, buffer_self_copy, ARITH_MAX},
         MutationResult, Mutator, Named,
     },
+    random_corpus_id,
     state::{HasCorpus, HasMaxSize, HasRand},
     Error,
 };
@@ -320,8 +321,7 @@ where
         let size = input.codes().len();
 
         // We don't want to use the testcase we're already using for splicing
-        let count = state.corpus().count();
-        let idx = state.rand_mut().below(count as u64) as usize;
+        let idx = random_corpus_id!(state.corpus(), state.rand_mut());
         if let Some(cur) = state.corpus().current() {
             if idx == *cur {
                 return Ok(MutationResult::Skipped);
@@ -397,8 +397,7 @@ where
         }
 
         // We don't want to use the testcase we're already using for splicing
-        let count = state.corpus().count();
-        let idx = state.rand_mut().below(count as u64) as usize;
+        let idx = random_corpus_id!(state.corpus(), state.rand_mut());
         if let Some(cur) = state.corpus().current() {
             if idx == *cur {
                 return Ok(MutationResult::Skipped);
diff --git a/libafl/src/mutators/gramatron.rs b/libafl/src/mutators/gramatron.rs
index 01ec4fa289..a1898dcbec 100644
--- a/libafl/src/mutators/gramatron.rs
+++ b/libafl/src/mutators/gramatron.rs
@@ -12,6 +12,7 @@ use crate::{
     generators::GramatronGenerator,
     inputs::{GramatronInput, Terminal, UsesInput},
     mutators::{MutationResult, Mutator},
+    random_corpus_id,
     state::{HasCorpus, HasMetadata, HasRand},
     Error,
 };
@@ -110,8 +111,7 @@ where
             return Ok(MutationResult::Skipped);
         }
 
-        let count = state.corpus().count();
-        let idx = state.rand_mut().below(count as u64) as usize;
+        let idx = random_corpus_id!(state.corpus(), state.rand_mut());
 
         let insert_at = state.rand_mut().below(input.terminals().len() as u64) as usize;
 
diff --git a/libafl/src/mutators/mod.rs b/libafl/src/mutators/mod.rs
index 6c71bad390..964c36641a 100644
--- a/libafl/src/mutators/mod.rs
+++ b/libafl/src/mutators/mod.rs
@@ -24,6 +24,7 @@ pub use nautilus::*;
 
 use crate::{
     bolts::tuples::{HasConstLen, Named},
+    corpus::CorpusId,
     inputs::UsesInput,
     Error,
 };
@@ -61,7 +62,7 @@ where
         &mut self,
         _state: &mut S,
         _stage_idx: i32,
-        _corpus_idx: Option<usize>,
+        _corpus_idx: Option<CorpusId>,
     ) -> Result<(), Error> {
         Ok(())
     }
@@ -85,7 +86,7 @@ where
         &mut self,
         state: &mut S,
         stage_idx: i32,
-        corpus_idx: Option<usize>,
+        corpus_idx: Option<CorpusId>,
     ) -> Result<(), Error>;
 
     /// Gets the [`Mutator`] at the given index and runs the `mutate` function on it.
@@ -103,7 +104,7 @@ where
         index: usize,
         state: &mut S,
         stage_idx: i32,
-        corpus_idx: Option<usize>,
+        corpus_idx: Option<CorpusId>,
     ) -> Result<(), Error>;
 }
 
@@ -124,7 +125,7 @@ where
         &mut self,
         _state: &mut S,
         _stage_idx: i32,
-        _corpus_idx: Option<usize>,
+        _corpus_idx: Option<CorpusId>,
     ) -> Result<(), Error> {
         Ok(())
     }
@@ -144,7 +145,7 @@ where
         _index: usize,
         _state: &mut S,
         _stage_idx: i32,
-        _corpus_idx: Option<usize>,
+        _corpus_idx: Option<CorpusId>,
     ) -> Result<(), Error> {
         Ok(())
     }
@@ -174,7 +175,7 @@ where
         &mut self,
         state: &mut S,
         stage_idx: i32,
-        corpus_idx: Option<usize>,
+        corpus_idx: Option<CorpusId>,
     ) -> Result<(), Error> {
         self.0.post_exec(state, stage_idx, corpus_idx)?;
         self.1.post_exec_all(state, stage_idx, corpus_idx)
@@ -199,7 +200,7 @@ where
         index: usize,
         state: &mut S,
         stage_idx: i32,
-        corpus_idx: Option<usize>,
+        corpus_idx: Option<CorpusId>,
     ) -> Result<(), Error> {
         if index == 0 {
             self.0.post_exec(state, stage_idx, corpus_idx)
@@ -218,6 +219,7 @@ pub mod pybind {
 
     use super::{MutationResult, Mutator};
     use crate::{
+        corpus::CorpusId,
         inputs::{BytesInput, HasBytesVec},
         mutators::scheduled::pybind::PythonStdHavocMutator,
         state::pybind::{PythonStdState, PythonStdStateWrapper},
@@ -263,13 +265,17 @@ pub mod pybind {
             &mut self,
             state: &mut PythonStdState,
             stage_idx: i32,
-            corpus_idx: Option<usize>,
+            corpus_idx: Option<CorpusId>,
         ) -> Result<(), Error> {
             Python::with_gil(|py| -> PyResult<()> {
                 self.inner.call_method1(
                     py,
                     "post_exec",
-                    (PythonStdStateWrapper::wrap(state), stage_idx, corpus_idx),
+                    (
+                        PythonStdStateWrapper::wrap(state),
+                        stage_idx,
+                        corpus_idx.map(|x| x.0),
+                    ),
                 )?;
                 Ok(())
             })?;
@@ -345,7 +351,7 @@ pub mod pybind {
             &mut self,
             state: &mut PythonStdState,
             stage_idx: i32,
-            corpus_idx: Option<usize>,
+            corpus_idx: Option<CorpusId>,
         ) -> Result<(), Error> {
             unwrap_me_mut!(self.wrapper, m, {
                 m.post_exec(state, stage_idx, corpus_idx)
diff --git a/libafl/src/mutators/mopt_mutator.rs b/libafl/src/mutators/mopt_mutator.rs
index 0dfc803a25..62d39bb5c4 100644
--- a/libafl/src/mutators/mopt_mutator.rs
+++ b/libafl/src/mutators/mopt_mutator.rs
@@ -9,7 +9,7 @@ use serde::{Deserialize, Serialize};
 
 use crate::{
     bolts::rands::{Rand, StdRand},
-    corpus::Corpus,
+    corpus::{Corpus, CorpusId},
     mutators::{ComposedByMutations, MutationResult, Mutator, MutatorsTuple, ScheduledMutator},
     state::{HasCorpus, HasMetadata, HasRand, HasSolutions},
     Error,
@@ -407,7 +407,7 @@ where
         &mut self,
         state: &mut S,
         _stage_idx: i32,
-        _corpus_idx: Option<usize>,
+        _corpus_idx: Option<CorpusId>,
     ) -> Result<(), Error> {
         let before = self.finds_before;
         let after = state.corpus().count() + state.solutions().count();
diff --git a/libafl/src/mutators/mutations.rs b/libafl/src/mutators/mutations.rs
index 3a2a612df4..48ae5ce8f4 100644
--- a/libafl/src/mutators/mutations.rs
+++ b/libafl/src/mutators/mutations.rs
@@ -11,6 +11,7 @@ use crate::{
     corpus::Corpus,
     inputs::{HasBytesVec, UsesInput},
     mutators::{MutationResult, Mutator},
+    random_corpus_id,
     state::{HasCorpus, HasMaxSize, HasRand},
     Error,
 };
@@ -912,8 +913,8 @@ where
         let size = input.bytes().len();
 
         // We don't want to use the testcase we're already using for splicing
-        let count = state.corpus().count();
-        let idx = state.rand_mut().below(count as u64) as usize;
+        let idx = random_corpus_id!(state.corpus(), state.rand_mut());
+
         if let Some(cur) = state.corpus().current() {
             if idx == *cur {
                 return Ok(MutationResult::Skipped);
@@ -990,8 +991,7 @@ where
         }
 
         // We don't want to use the testcase we're already using for splicing
-        let count = state.corpus().count();
-        let idx = state.rand_mut().below(count as u64) as usize;
+        let idx = random_corpus_id!(state.corpus(), state.rand_mut());
         if let Some(cur) = state.corpus().current() {
             if idx == *cur {
                 return Ok(MutationResult::Skipped);
@@ -1069,8 +1069,7 @@ where
         _stage_idx: i32,
     ) -> Result<MutationResult, Error> {
         // We don't want to use the testcase we're already using for splicing
-        let count = state.corpus().count();
-        let idx = state.rand_mut().below(count as u64) as usize;
+        let idx = random_corpus_id!(state.corpus(), state.rand_mut());
         if let Some(cur) = state.corpus().current() {
             if idx == *cur {
                 return Ok(MutationResult::Skipped);
diff --git a/libafl/src/mutators/scheduled.rs b/libafl/src/mutators/scheduled.rs
index e60318132a..edc483f505 100644
--- a/libafl/src/mutators/scheduled.rs
+++ b/libafl/src/mutators/scheduled.rs
@@ -15,7 +15,7 @@ use crate::{
         tuples::{tuple_list, tuple_list_type, NamedTuple},
         AsMutSlice, AsSlice,
     },
-    corpus::Corpus,
+    corpus::{Corpus, CorpusId},
     inputs::UsesInput,
     mutators::{MutationResult, Mutator, MutatorsTuple},
     state::{HasCorpus, HasMetadata, HasRand, State},
@@ -321,7 +321,7 @@ where
         &mut self,
         state: &mut S,
         _stage_idx: i32,
-        corpus_idx: Option<usize>,
+        corpus_idx: Option<CorpusId>,
     ) -> Result<(), Error> {
         if let Some(idx) = corpus_idx {
             let mut testcase = (*state.corpus_mut().get(idx)?).borrow_mut();
@@ -441,7 +441,9 @@ mod tests {
             .add(Testcase::new(vec![b'd', b'e', b'f'].into()))
             .unwrap();
 
-        let testcase = corpus.get(0).expect("Corpus did not contain entries");
+        let testcase = corpus
+            .get(corpus.first().unwrap())
+            .expect("Corpus did not contain entries");
         let mut input = testcase.borrow_mut().load_input().unwrap().clone();
 
         let mut feedback = ConstFeedback::new(false);
@@ -481,7 +483,9 @@ mod tests {
             .add(Testcase::new(vec![b'd', b'e', b'f'].into()))
             .unwrap();
 
-        let testcase = corpus.get(0).expect("Corpus did not contain entries");
+        let testcase = corpus
+            .get(corpus.first().unwrap())
+            .expect("Corpus did not contain entries");
         let mut input = testcase.borrow_mut().load_input().unwrap().clone();
         let input_prior = input.clone();
 
diff --git a/libafl/src/schedulers/accounting.rs b/libafl/src/schedulers/accounting.rs
index 04b4fbde9a..643175348b 100644
--- a/libafl/src/schedulers/accounting.rs
+++ b/libafl/src/schedulers/accounting.rs
@@ -8,7 +8,7 @@ use serde::{Deserialize, Serialize};
 
 use crate::{
     bolts::{rands::Rand, AsMutSlice, AsSlice, HasLen, HasRefCnt},
-    corpus::{Corpus, Testcase},
+    corpus::{Corpus, CorpusId, Testcase},
     feedbacks::MapIndexesMetadata,
     inputs::UsesInput,
     schedulers::{
@@ -74,7 +74,7 @@ impl AccountingIndexesMetadata {
 #[derive(Debug, Serialize, Deserialize)]
 pub struct TopAccountingMetadata {
     /// map index -> corpus index
-    pub map: HashMap<usize, usize>,
+    pub map: HashMap<usize, CorpusId>,
     /// If changed sicne the previous add to the corpus
     pub changed: bool,
     /// The max accounting seen so far
@@ -125,7 +125,7 @@ where
     CS::State: HasCorpus + HasMetadata + HasRand + Debug,
     <CS::State as UsesInput>::Input: HasLen,
 {
-    fn on_add(&self, state: &mut Self::State, idx: usize) -> Result<(), Error> {
+    fn on_add(&self, state: &mut Self::State, idx: CorpusId) -> Result<(), Error> {
         self.update_accounting_score(state, idx)?;
         self.inner.on_add(state, idx)
     }
@@ -133,7 +133,7 @@ where
     fn on_replace(
         &self,
         state: &mut Self::State,
-        idx: usize,
+        idx: CorpusId,
         testcase: &Testcase<<Self::State as UsesInput>::Input>,
     ) -> Result<(), Error> {
         self.inner.on_replace(state, idx, testcase)
@@ -142,13 +142,13 @@ where
     fn on_remove(
         &self,
         state: &mut Self::State,
-        idx: usize,
+        idx: CorpusId,
         testcase: &Option<Testcase<<Self::State as UsesInput>::Input>>,
     ) -> Result<(), Error> {
         self.inner.on_remove(state, idx, testcase)
     }
 
-    fn next(&self, state: &mut Self::State) -> Result<usize, Error> {
+    fn next(&self, state: &mut Self::State) -> Result<CorpusId, Error> {
         if state
             .metadata()
             .get::<TopAccountingMetadata>()
@@ -183,7 +183,11 @@ where
     /// Update the `Corpus` score
     #[allow(clippy::unused_self)]
     #[allow(clippy::cast_possible_wrap)]
-    pub fn update_accounting_score(&self, state: &mut CS::State, idx: usize) -> Result<(), Error> {
+    pub fn update_accounting_score(
+        &self,
+        state: &mut CS::State,
+        idx: CorpusId,
+    ) -> Result<(), Error> {
         let mut indexes = vec![];
         let mut new_favoreds = vec![];
         {
diff --git a/libafl/src/schedulers/minimizer.rs b/libafl/src/schedulers/minimizer.rs
index 76d381dc56..87c21c3738 100644
--- a/libafl/src/schedulers/minimizer.rs
+++ b/libafl/src/schedulers/minimizer.rs
@@ -9,7 +9,7 @@ use serde::{Deserialize, Serialize};
 
 use crate::{
     bolts::{rands::Rand, serdeany::SerdeAny, AsSlice, HasRefCnt},
-    corpus::{Corpus, Testcase},
+    corpus::{Corpus, CorpusId, Testcase},
     feedbacks::MapIndexesMetadata,
     inputs::UsesInput,
     schedulers::{LenTimeMulTestcaseScore, Scheduler, TestcaseScore},
@@ -30,7 +30,7 @@ crate::impl_serdeany!(IsFavoredMetadata);
 #[derive(Debug, Serialize, Deserialize)]
 pub struct TopRatedsMetadata {
     /// map index -> corpus index
-    pub map: HashMap<usize, usize>,
+    pub map: HashMap<usize, CorpusId>,
 }
 
 crate::impl_serdeany!(TopRatedsMetadata);
@@ -46,7 +46,7 @@ impl TopRatedsMetadata {
 
     /// Getter for map
     #[must_use]
-    pub fn map(&self) -> &HashMap<usize, usize> {
+    pub fn map(&self) -> &HashMap<usize, CorpusId> {
         &self.map
     }
 }
@@ -82,7 +82,7 @@ where
     CS::State: HasCorpus + HasMetadata + HasRand,
 {
     /// Add an entry to the corpus and return its index
-    fn on_add(&self, state: &mut CS::State, idx: usize) -> Result<(), Error> {
+    fn on_add(&self, state: &mut CS::State, idx: CorpusId) -> Result<(), Error> {
         self.update_score(state, idx)?;
         self.base.on_add(state, idx)
     }
@@ -91,7 +91,7 @@ where
     fn on_replace(
         &self,
         state: &mut CS::State,
-        idx: usize,
+        idx: CorpusId,
         testcase: &Testcase<<CS::State as UsesInput>::Input>,
     ) -> Result<(), Error> {
         self.update_score(state, idx)?;
@@ -102,7 +102,7 @@ where
     fn on_remove(
         &self,
         state: &mut CS::State,
-        idx: usize,
+        idx: CorpusId,
         testcase: &Option<Testcase<<CS::State as UsesInput>::Input>>,
     ) -> Result<(), Error> {
         self.base.on_remove(state, idx, testcase)?;
@@ -112,19 +112,13 @@ where
                 .drain_filter(|_, other_idx| *other_idx == idx)
                 .map(|(entry, _)| entry)
                 .collect::<Vec<_>>();
-            meta.map
-                .values_mut()
-                .filter(|other_idx| **other_idx > idx)
-                .for_each(|other_idx| {
-                    *other_idx -= 1;
-                });
             entries
         } else {
             return Ok(());
         };
         entries.sort_unstable(); // this should already be sorted, but just in case
         let mut map = HashMap::new();
-        for i in 0..state.corpus().count() {
+        for i in state.corpus().ids() {
             let mut old = state.corpus().get(i)?.borrow_mut();
             let factor = F::compute(&mut *old, state)?;
             if let Some(old_map) = old.metadata_mut().get_mut::<M>() {
@@ -169,7 +163,7 @@ where
     }
 
     /// Gets the next entry
-    fn next(&self, state: &mut CS::State) -> Result<usize, Error> {
+    fn next(&self, state: &mut CS::State) -> Result<CorpusId, Error> {
         self.cull(state)?;
         let mut idx = self.base.next(state)?;
         while {
@@ -197,7 +191,7 @@ where
     /// Update the `Corpus` score using the `MinimizerScheduler`
     #[allow(clippy::unused_self)]
     #[allow(clippy::cast_possible_wrap)]
-    pub fn update_score(&self, state: &mut CS::State, idx: usize) -> Result<(), Error> {
+    pub fn update_score(&self, state: &mut CS::State, idx: CorpusId) -> Result<(), Error> {
         // Create a new top rated meta if not existing
         if state.metadata().get::<TopRatedsMetadata>().is_none() {
             state.add_metadata(TopRatedsMetadata::new());
diff --git a/libafl/src/schedulers/mod.rs b/libafl/src/schedulers/mod.rs
index 9d3cdfd8f3..2a0a96ea99 100644
--- a/libafl/src/schedulers/mod.rs
+++ b/libafl/src/schedulers/mod.rs
@@ -1,39 +1,39 @@
 //! Schedule the access to the Corpus.
 
-pub mod queue;
+use alloc::borrow::ToOwned;
 use core::marker::PhantomData;
 
+pub mod testcase_score;
+pub use testcase_score::{LenTimeMulTestcaseScore, TestcaseScore};
+
+pub mod queue;
 pub use queue::QueueScheduler;
 
+pub mod minimizer;
+pub use minimizer::{
+    IndexesLenTimeMinimizerScheduler, LenTimeMinimizerScheduler, MinimizerScheduler,
+};
+
+pub mod powersched;
+pub use powersched::PowerQueueScheduler;
+
 pub mod probabilistic_sampling;
 pub use probabilistic_sampling::ProbabilitySamplingScheduler;
 
 pub mod accounting;
 pub use accounting::CoverageAccountingScheduler;
 
-pub mod testcase_score;
-pub use testcase_score::{LenTimeMulTestcaseScore, TestcaseScore};
-
-pub mod minimizer;
-pub use minimizer::{
-    IndexesLenTimeMinimizerScheduler, LenTimeMinimizerScheduler, MinimizerScheduler,
-};
-
 pub mod weighted;
 pub use weighted::{StdWeightedScheduler, WeightedScheduler};
 
-pub mod powersched;
-use alloc::borrow::ToOwned;
-
-pub use powersched::PowerQueueScheduler;
-
 pub mod tuneable;
 pub use tuneable::*;
 
 use crate::{
     bolts::rands::Rand,
-    corpus::{Corpus, Testcase},
+    corpus::{Corpus, CorpusId, Testcase},
     inputs::UsesInput,
+    random_corpus_id,
     state::{HasCorpus, HasRand, UsesState},
     Error,
 };
@@ -42,7 +42,7 @@ use crate::{
 /// It has hooks to corpus add/replace/remove to allow complex scheduling algorithms to collect data.
 pub trait Scheduler: UsesState {
     /// Added an entry to the corpus at the given index
-    fn on_add(&self, _state: &mut Self::State, _idx: usize) -> Result<(), Error> {
+    fn on_add(&self, _state: &mut Self::State, _idx: CorpusId) -> Result<(), Error> {
         Ok(())
     }
 
@@ -50,7 +50,7 @@ pub trait Scheduler: UsesState {
     fn on_replace(
         &self,
         _state: &mut Self::State,
-        _idx: usize,
+        _idx: CorpusId,
         _prev: &Testcase<<Self::State as UsesInput>::Input>,
     ) -> Result<(), Error> {
         Ok(())
@@ -60,14 +60,14 @@ pub trait Scheduler: UsesState {
     fn on_remove(
         &self,
         _state: &mut Self::State,
-        _idx: usize,
+        _idx: CorpusId,
         _testcase: &Option<Testcase<<Self::State as UsesInput>::Input>>,
     ) -> Result<(), Error> {
         Ok(())
     }
 
     /// Gets the next entry
-    fn next(&self, state: &mut Self::State) -> Result<usize, Error>;
+    fn next(&self, state: &mut Self::State) -> Result<CorpusId, Error>;
 }
 
 /// Feed the fuzzer simply with a random testcase on request
@@ -88,12 +88,11 @@ where
     S: HasCorpus + HasRand,
 {
     /// Gets the next entry at random
-    fn next(&self, state: &mut Self::State) -> Result<usize, Error> {
+    fn next(&self, state: &mut Self::State) -> Result<CorpusId, Error> {
         if state.corpus().count() == 0 {
             Err(Error::empty("No entries in corpus".to_owned()))
         } else {
-            let len = state.corpus().count();
-            let id = state.rand_mut().below(len as u64) as usize;
+            let id = random_corpus_id!(state.corpus(), state.rand_mut());
             *state.corpus_mut().current_mut() = Some(id);
             Ok(id)
         }
diff --git a/libafl/src/schedulers/powersched.rs b/libafl/src/schedulers/powersched.rs
index 6278d92811..fca5719aa9 100644
--- a/libafl/src/schedulers/powersched.rs
+++ b/libafl/src/schedulers/powersched.rs
@@ -9,7 +9,7 @@ use core::{marker::PhantomData, time::Duration};
 use serde::{Deserialize, Serialize};
 
 use crate::{
-    corpus::{Corpus, SchedulerTestcaseMetaData},
+    corpus::{Corpus, CorpusId, SchedulerTestcaseMetaData},
     inputs::UsesInput,
     schedulers::Scheduler,
     state::{HasCorpus, HasMetadata, UsesState},
@@ -180,7 +180,7 @@ where
     S: HasCorpus + HasMetadata,
 {
     /// Add an entry to the corpus and return its index
-    fn on_add(&self, state: &mut Self::State, idx: usize) -> Result<(), Error> {
+    fn on_add(&self, state: &mut Self::State, idx: CorpusId) -> Result<(), Error> {
         if !state.has_metadata::<SchedulerMetadata>() {
             state.add_metadata::<SchedulerMetadata>(SchedulerMetadata::new(Some(self.strat)));
         }
@@ -211,13 +211,15 @@ where
         Ok(())
     }
 
-    fn next(&self, state: &mut Self::State) -> Result<usize, Error> {
+    fn next(&self, state: &mut Self::State) -> Result<CorpusId, Error> {
         if state.corpus().count() == 0 {
             Err(Error::empty(String::from("No entries in corpus")))
         } else {
             let id = match state.corpus().current() {
                 Some(cur) => {
-                    if *cur + 1 >= state.corpus().count() {
+                    if let Some(next) = state.corpus().next(*cur) {
+                        next
+                    } else {
                         let psmeta = state
                             .metadata_mut()
                             .get_mut::<SchedulerMetadata>()
@@ -225,12 +227,10 @@ where
                                 Error::key_not_found("SchedulerMetadata not found".to_string())
                             })?;
                         psmeta.set_queue_cycles(psmeta.queue_cycles() + 1);
-                        0
-                    } else {
-                        *cur + 1
+                        state.corpus().first().unwrap()
                     }
                 }
-                None => 0,
+                None => state.corpus().first().unwrap(),
             };
             *state.corpus_mut().current_mut() = Some(id);
 
diff --git a/libafl/src/schedulers/probabilistic_sampling.rs b/libafl/src/schedulers/probabilistic_sampling.rs
index fd17758a9c..aaacc9f847 100644
--- a/libafl/src/schedulers/probabilistic_sampling.rs
+++ b/libafl/src/schedulers/probabilistic_sampling.rs
@@ -9,7 +9,7 @@ use serde::{Deserialize, Serialize};
 
 use crate::{
     bolts::rands::Rand,
-    corpus::Corpus,
+    corpus::{Corpus, CorpusId},
     inputs::UsesInput,
     schedulers::{Scheduler, TestcaseScore},
     state::{HasCorpus, HasMetadata, HasRand, UsesState},
@@ -29,7 +29,7 @@ where
 #[derive(Debug, Serialize, Deserialize)]
 pub struct ProbabilityMetadata {
     /// corpus index -> probability
-    pub map: HashMap<usize, f64>,
+    pub map: HashMap<CorpusId, f64>,
     /// total probability of all items in the map
     pub total_probability: f64,
 }
@@ -69,7 +69,7 @@ where
     /// Calculate the score and store in `ProbabilityMetadata`
     #[allow(clippy::cast_precision_loss)]
     #[allow(clippy::unused_self)]
-    pub fn store_probability(&self, state: &mut S, idx: usize) -> Result<(), Error> {
+    pub fn store_probability(&self, state: &mut S, idx: CorpusId) -> Result<(), Error> {
         let factor = F::compute(&mut *state.corpus().get(idx)?.borrow_mut(), state)?;
         if factor == 0.0 {
             return Err(Error::illegal_state(
@@ -99,7 +99,7 @@ where
     F: TestcaseScore<S>,
     S: HasCorpus + HasMetadata + HasRand,
 {
-    fn on_add(&self, state: &mut Self::State, idx: usize) -> Result<(), Error> {
+    fn on_add(&self, state: &mut Self::State, idx: CorpusId) -> Result<(), Error> {
         if state.metadata().get::<ProbabilityMetadata>().is_none() {
             state.add_metadata(ProbabilityMetadata::new());
         }
@@ -108,7 +108,7 @@ where
 
     /// Gets the next entry
     #[allow(clippy::cast_precision_loss)]
-    fn next(&self, state: &mut Self::State) -> Result<usize, Error> {
+    fn next(&self, state: &mut Self::State) -> Result<CorpusId, Error> {
         if state.corpus().count() == 0 {
             Err(Error::empty(String::from("No entries in corpus")))
         } else {
diff --git a/libafl/src/schedulers/queue.rs b/libafl/src/schedulers/queue.rs
index 4f0cd0fb81..f0190c0b93 100644
--- a/libafl/src/schedulers/queue.rs
+++ b/libafl/src/schedulers/queue.rs
@@ -4,7 +4,7 @@ use alloc::borrow::ToOwned;
 use core::marker::PhantomData;
 
 use crate::{
-    corpus::Corpus,
+    corpus::{Corpus, CorpusId},
     inputs::UsesInput,
     schedulers::Scheduler,
     state::{HasCorpus, UsesState},
@@ -29,20 +29,16 @@ where
     S: HasCorpus,
 {
     /// Gets the next entry in the queue
-    fn next(&self, state: &mut Self::State) -> Result<usize, Error> {
+    fn next(&self, state: &mut Self::State) -> Result<CorpusId, Error> {
         if state.corpus().count() == 0 {
             Err(Error::empty("No entries in corpus".to_owned()))
         } else {
-            let id = match state.corpus().current() {
-                Some(cur) => {
-                    if *cur + 1 >= state.corpus().count() {
-                        0
-                    } else {
-                        *cur + 1
-                    }
-                }
-                None => 0,
-            };
+            let id = state
+                .corpus()
+                .current()
+                .map(|id| state.corpus().next(id))
+                .flatten()
+                .unwrap_or_else(|| state.corpus().first().unwrap());
             *state.corpus_mut().current_mut() = Some(id);
             Ok(id)
         }
diff --git a/libafl/src/schedulers/testcase_score.rs b/libafl/src/schedulers/testcase_score.rs
index f9c21b262f..2593cd9be6 100644
--- a/libafl/src/schedulers/testcase_score.rs
+++ b/libafl/src/schedulers/testcase_score.rs
@@ -77,7 +77,7 @@ where
                 let mut n_paths = 0;
                 let mut v = 0.0;
                 let cur_index = state.corpus().current().unwrap();
-                for idx in 0..corpus.count() {
+                for idx in corpus.ids() {
                     let n_fuzz_entry = if cur_index == idx {
                         entry
                             .metadata()
diff --git a/libafl/src/schedulers/tuneable.rs b/libafl/src/schedulers/tuneable.rs
index e2cd11b35e..cc3a0a1fa5 100644
--- a/libafl/src/schedulers/tuneable.rs
+++ b/libafl/src/schedulers/tuneable.rs
@@ -8,7 +8,7 @@ use core::marker::PhantomData;
 use serde::{Deserialize, Serialize};
 
 use crate::{
-    corpus::Corpus,
+    corpus::{Corpus, CorpusId},
     impl_serdeany,
     inputs::UsesInput,
     schedulers::Scheduler,
@@ -18,7 +18,7 @@ use crate::{
 
 #[derive(Default, Clone, Copy, Eq, PartialEq, Debug, Serialize, Deserialize)]
 struct TuneableSchedulerMetadata {
-    next: Option<usize>,
+    next: Option<CorpusId>,
 }
 
 impl_serdeany!(TuneableSchedulerMetadata);
@@ -57,12 +57,12 @@ where
     }
 
     /// Sets the next corpus id to be used
-    pub fn set_next(state: &mut S, next: usize) {
+    pub fn set_next(state: &mut S, next: CorpusId) {
         Self::metadata_mut(state).next = Some(next);
     }
 
     /// Gets the next set corpus id
-    pub fn get_next(state: &S) -> Option<usize> {
+    pub fn get_next(state: &S) -> Option<CorpusId> {
         Self::metadata(state).next
     }
 
@@ -73,8 +73,11 @@ where
     }
 
     /// Gets the current corpus entry id
-    pub fn get_current(state: &S) -> usize {
-        state.corpus().current().unwrap_or_default()
+    pub fn get_current(state: &S) -> CorpusId {
+        state
+            .corpus()
+            .current()
+            .unwrap_or_else(|| state.corpus().first().expect("Empty corpus"))
     }
 }
 
@@ -90,17 +93,17 @@ where
     S: HasCorpus + HasMetadata,
 {
     /// Gets the next entry in the queue
-    fn next(&self, state: &mut Self::State) -> Result<usize, Error> {
+    fn next(&self, state: &mut Self::State) -> Result<CorpusId, Error> {
         if state.corpus().count() == 0 {
             return Err(Error::empty("No entries in corpus".to_owned()));
         }
         let id = if let Some(next) = Self::get_next(state) {
             // next was set
             next
-        } else if Self::get_current(state) + 1 >= state.corpus().count() {
-            0
+        } else if let Some(next) = state.corpus().next(Self::get_current(state)) {
+            next
         } else {
-            Self::get_current(state) + 1
+            state.corpus().first().unwrap()
         };
         *state.corpus_mut().current_mut() = Some(id);
         Ok(id)
diff --git a/libafl/src/schedulers/weighted.rs b/libafl/src/schedulers/weighted.rs
index 4efed1dd96..9a5586704f 100644
--- a/libafl/src/schedulers/weighted.rs
+++ b/libafl/src/schedulers/weighted.rs
@@ -1,18 +1,17 @@
 //! The queue corpus scheduler with weighted queue item selection from aflpp (`https://github.com/AFLplusplus/AFLplusplus/blob/1d4f1e48797c064ee71441ba555b29fc3f467983/src/afl-fuzz-queue.c#L32`)
 //! This queue corpus scheduler needs calibration stage.
 
-use alloc::{
-    string::{String, ToString},
-    vec::Vec,
-};
+use alloc::string::{String, ToString};
 use core::marker::PhantomData;
 
+use hashbrown::HashMap;
 use serde::{Deserialize, Serialize};
 
 use crate::{
     bolts::rands::Rand,
-    corpus::{Corpus, SchedulerTestcaseMetaData, Testcase},
+    corpus::{Corpus, CorpusId, SchedulerTestcaseMetaData, Testcase},
     inputs::UsesInput,
+    random_corpus_id,
     schedulers::{
         powersched::{PowerSchedule, SchedulerMetadata},
         testcase_score::{CorpusWeightTestcaseScore, TestcaseScore},
@@ -29,9 +28,9 @@ pub struct WeightedScheduleMetadata {
     /// The fuzzer execution spent in the current cycles
     runs_in_current_cycle: usize,
     /// Alias table for weighted queue entry selection
-    alias_table: Vec<usize>,
+    alias_table: HashMap<CorpusId, CorpusId>,
     /// Probability for which queue entry is selected
-    alias_probability: Vec<f64>,
+    alias_probability: HashMap<CorpusId, f64>,
 }
 
 impl Default for WeightedScheduleMetadata {
@@ -46,8 +45,8 @@ impl WeightedScheduleMetadata {
     pub fn new() -> Self {
         Self {
             runs_in_current_cycle: 0,
-            alias_table: vec![0],
-            alias_probability: vec![0.0],
+            alias_table: HashMap::default(),
+            alias_probability: HashMap::default(),
         }
     }
 
@@ -64,23 +63,23 @@ impl WeightedScheduleMetadata {
 
     /// The getter for `alias_table`
     #[must_use]
-    pub fn alias_table(&self) -> &[usize] {
+    pub fn alias_table(&self) -> &HashMap<CorpusId, CorpusId> {
         &self.alias_table
     }
 
     /// The setter for `alias_table`
-    pub fn set_alias_table(&mut self, table: Vec<usize>) {
+    pub fn set_alias_table(&mut self, table: HashMap<CorpusId, CorpusId>) {
         self.alias_table = table;
     }
 
     /// The getter for `alias_probability`
     #[must_use]
-    pub fn alias_probability(&self) -> &[f64] {
+    pub fn alias_probability(&self) -> &HashMap<CorpusId, f64> {
         &self.alias_probability
     }
 
     /// The setter for `alias_probability`
-    pub fn set_alias_probability(&mut self, probability: Vec<f64>) {
+    pub fn set_alias_probability(&mut self, probability: HashMap<CorpusId, f64>) {
         self.alias_probability = probability;
     }
 }
@@ -137,25 +136,25 @@ where
     pub fn create_alias_table(&self, state: &mut S) -> Result<(), Error> {
         let n = state.corpus().count();
 
-        let mut alias_table: Vec<usize> = vec![0; n];
-        let mut alias_probability: Vec<f64> = vec![0.0; n];
-        let mut weights: Vec<f64> = vec![0.0; n];
+        let mut alias_table: HashMap<CorpusId, CorpusId> = HashMap::default();
+        let mut alias_probability: HashMap<CorpusId, f64> = HashMap::default();
+        let mut weights: HashMap<CorpusId, f64> = HashMap::default();
 
-        let mut p_arr: Vec<f64> = vec![0.0; n];
-        let mut s_arr: Vec<usize> = vec![0; n];
-        let mut l_arr: Vec<usize> = vec![0; n];
+        let mut p_arr: HashMap<CorpusId, f64> = HashMap::default();
+        let mut s_arr: HashMap<usize, CorpusId> = HashMap::default();
+        let mut l_arr: HashMap<usize, CorpusId> = HashMap::default();
 
         let mut sum: f64 = 0.0;
 
-        for (i, item) in weights.iter_mut().enumerate().take(n) {
+        for i in state.corpus().ids() {
             let mut testcase = state.corpus().get(i)?.borrow_mut();
             let weight = F::compute(&mut *testcase, state)?;
-            *item = weight;
+            weights.insert(i, weight);
             sum += weight;
         }
 
-        for i in 0..n {
-            p_arr[i] = weights[i] * (n as f64) / sum;
+        for (i, w) in weights.iter() {
+            p_arr.insert(*i, w * (n as f64) / sum);
         }
 
         // # of items in queue S
@@ -164,12 +163,12 @@ where
         // # of items in queue L
         let mut n_l = 0;
         // Divide P into two queues, S and L
-        for s in (0..n).rev() {
-            if p_arr[s] < 1.0 {
-                s_arr[n_s] = s;
+        for s in state.corpus().ids().rev() {
+            if *p_arr.get(&s).unwrap() < 1.0 {
+                s_arr.insert(n_s, s);
                 n_s += 1;
             } else {
-                l_arr[n_l] = s;
+                l_arr.insert(n_l, s);
                 n_l += 1;
             }
         }
@@ -177,30 +176,30 @@ where
         while n_s > 0 && n_l > 0 {
             n_s -= 1;
             n_l -= 1;
-            let a = s_arr[n_s];
-            let g = l_arr[n_l];
+            let a = *s_arr.get(&n_s).unwrap();
+            let g = *l_arr.get(&n_l).unwrap();
 
-            alias_probability[a] = p_arr[a];
-            alias_table[a] = g;
-            p_arr[g] = p_arr[g] + p_arr[a] - 1.0;
+            alias_probability.insert(a, *p_arr.get(&a).unwrap());
+            alias_table.insert(a, g);
+            *p_arr.get_mut(&g).unwrap() += p_arr.get(&a).unwrap() - 1.0;
 
-            if p_arr[g] < 1.0 {
-                s_arr[n_s] = g;
+            if *p_arr.get(&g).unwrap() < 1.0 {
+                *s_arr.get_mut(&n_s).unwrap() = g;
                 n_s += 1;
             } else {
-                l_arr[n_l] = g;
+                *l_arr.get_mut(&n_l).unwrap() = g;
                 n_l += 1;
             }
         }
 
         while n_l > 0 {
             n_l -= 1;
-            alias_probability[l_arr[n_l]] = 1.0;
+            alias_probability.insert(*l_arr.get(&n_l).unwrap(), 1.0);
         }
 
         while n_s > 0 {
             n_s -= 1;
-            alias_probability[s_arr[n_s]] = 1.0;
+            alias_probability.insert(*s_arr.get(&n_s).unwrap(), 1.0);
         }
 
         let wsmeta = state
@@ -230,7 +229,7 @@ where
     S: HasCorpus + HasMetadata + HasRand,
 {
     /// Add an entry to the corpus and return its index
-    fn on_add(&self, state: &mut S, idx: usize) -> Result<(), Error> {
+    fn on_add(&self, state: &mut S, idx: CorpusId) -> Result<(), Error> {
         if !state.has_metadata::<SchedulerMetadata>() {
             state.add_metadata(SchedulerMetadata::new(self.strat));
         }
@@ -271,7 +270,7 @@ where
     fn on_replace(
         &self,
         state: &mut S,
-        idx: usize,
+        idx: CorpusId,
         _testcase: &Testcase<S::Input>,
     ) -> Result<(), Error> {
         // Recreate the alias table
@@ -281,7 +280,7 @@ where
     fn on_remove(
         &self,
         state: &mut S,
-        _idx: usize,
+        _idx: CorpusId,
         _testcase: &Option<Testcase<S::Input>>,
     ) -> Result<(), Error> {
         // Recreate the alias table
@@ -290,12 +289,13 @@ where
     }
 
     #[allow(clippy::similar_names, clippy::cast_precision_loss)]
-    fn next(&self, state: &mut S) -> Result<usize, Error> {
-        if state.corpus().count() == 0 {
+    fn next(&self, state: &mut S) -> Result<CorpusId, Error> {
+        let corpus_counts = state.corpus().count();
+        if corpus_counts == 0 {
             Err(Error::empty(String::from("No entries in corpus")))
         } else {
-            let corpus_counts = state.corpus().count();
-            let s = state.rand_mut().below(corpus_counts as u64) as usize;
+            let s = random_corpus_id!(state.corpus(), state.rand_mut());
+
             // Choose a random value between 0.000000000 and 1.000000000
             let probability = state.rand_mut().between(0, 1000000000) as f64 / 1000000000_f64;
 
@@ -308,16 +308,17 @@ where
 
             let current_cycles = wsmeta.runs_in_current_cycle();
 
+            // TODO deal with corpus_counts decreasing due to removals
             if current_cycles >= corpus_counts {
                 wsmeta.set_runs_current_cycle(0);
             } else {
                 wsmeta.set_runs_current_cycle(current_cycles + 1);
             }
 
-            let idx = if probability < wsmeta.alias_probability()[s] {
+            let idx = if probability < *wsmeta.alias_probability().get(&s).unwrap() {
                 s
             } else {
-                wsmeta.alias_table()[s]
+                *wsmeta.alias_table().get(&s).unwrap()
             };
 
             // Update depth
diff --git a/libafl/src/stages/calibrate.rs b/libafl/src/stages/calibrate.rs
index ba093c6c3b..3a9fbc9c86 100644
--- a/libafl/src/stages/calibrate.rs
+++ b/libafl/src/stages/calibrate.rs
@@ -12,7 +12,7 @@ use serde::{Deserialize, Serialize};
 
 use crate::{
     bolts::{current_time, tuples::Named, AsIter},
-    corpus::{Corpus, SchedulerTestcaseMetaData},
+    corpus::{Corpus, CorpusId, SchedulerTestcaseMetaData},
     events::{EventFirer, LogSeverity},
     executors::{Executor, ExitKind, HasObservers},
     feedbacks::{
@@ -103,7 +103,7 @@ where
         executor: &mut E,
         state: &mut E::State,
         mgr: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         // Run this stage only once for each corpus entry
         if state.corpus().get(corpus_idx)?.borrow_mut().fuzz_level() > 0 {
diff --git a/libafl/src/stages/concolic.rs b/libafl/src/stages/concolic.rs
index 3332c52752..c6564153e7 100644
--- a/libafl/src/stages/concolic.rs
+++ b/libafl/src/stages/concolic.rs
@@ -9,7 +9,7 @@ use core::marker::PhantomData;
 
 use super::{Stage, TracingStage};
 use crate::{
-    corpus::Corpus,
+    corpus::{Corpus, CorpusId},
     executors::{Executor, HasObservers},
     observers::concolic::ConcolicObserver,
     state::{HasClientPerfMonitor, HasCorpus, HasExecutions, HasMetadata},
@@ -45,7 +45,7 @@ where
         executor: &mut E,
         state: &mut TE::State,
         manager: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         self.inner
             .perform(fuzzer, executor, state, manager, corpus_idx)?;
@@ -361,7 +361,7 @@ where
         executor: &mut E,
         state: &mut Z::State,
         manager: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         start_timer!(state);
         let testcase = state.corpus().get(corpus_idx)?.clone();
diff --git a/libafl/src/stages/dump.rs b/libafl/src/stages/dump.rs
index 194c611998..585533fddb 100644
--- a/libafl/src/stages/dump.rs
+++ b/libafl/src/stages/dump.rs
@@ -7,7 +7,7 @@ use std::{fs, fs::File, io::Write, path::PathBuf};
 use serde::{Deserialize, Serialize};
 
 use crate::{
-    corpus::Corpus,
+    corpus::{Corpus, CorpusId},
     inputs::UsesInput,
     stages::Stage,
     state::{HasCorpus, HasMetadata, HasRand, HasSolutions, UsesState},
@@ -17,8 +17,8 @@ use crate::{
 /// Metadata used to store information about disk dump indexes for names
 #[derive(Default, Serialize, Deserialize, Clone, Debug)]
 pub struct DumpToDiskMetadata {
-    last_corpus: usize,
-    last_solution: usize,
+    last_corpus: Option<CorpusId>,
+    last_solution: Option<CorpusId>,
 }
 
 crate::impl_serdeany!(DumpToDiskMetadata);
@@ -54,17 +54,19 @@ where
         _executor: &mut E,
         state: &mut Z::State,
         _manager: &mut EM,
-        _corpus_idx: usize,
+        _corpus_idx: CorpusId,
     ) -> Result<(), Error> {
-        let meta = state
-            .metadata()
-            .get::<DumpToDiskMetadata>()
-            .map_or_else(DumpToDiskMetadata::default, Clone::clone);
+        let (mut corpus_idx, mut solutions_idx) =
+            if let Some(meta) = state.metadata().get::<DumpToDiskMetadata>() {
+                (
+                    meta.last_corpus.and_then(|x| state.corpus().next(x)),
+                    meta.last_solution.and_then(|x| state.solutions().next(x)),
+                )
+            } else {
+                (state.corpus().first(), state.solutions().first())
+            };
 
-        let corpus_count = state.corpus().count();
-        let solutions_count = state.solutions().count();
-
-        for i in meta.last_corpus..corpus_count {
+        while let Some(i) = corpus_idx {
             let mut testcase = state.corpus().get(i)?.borrow_mut();
             let input = testcase.load_input()?;
             let bytes = (self.to_bytes)(input);
@@ -72,9 +74,11 @@ where
             let fname = self.corpus_dir.join(format!("id_{i}"));
             let mut f = File::create(fname)?;
             drop(f.write_all(&bytes));
+
+            corpus_idx = state.corpus().next(i);
         }
 
-        for i in meta.last_solution..solutions_count {
+        while let Some(i) = solutions_idx {
             let mut testcase = state.solutions().get(i)?.borrow_mut();
             let input = testcase.load_input()?;
             let bytes = (self.to_bytes)(input);
@@ -82,11 +86,13 @@ where
             let fname = self.solutions_dir.join(format!("id_{i}"));
             let mut f = File::create(fname)?;
             drop(f.write_all(&bytes));
+
+            solutions_idx = state.solutions().next(i);
         }
 
         state.add_metadata(DumpToDiskMetadata {
-            last_corpus: corpus_count,
-            last_solution: solutions_count,
+            last_corpus: state.corpus().last(),
+            last_solution: state.solutions().last(),
         });
 
         Ok(())
diff --git a/libafl/src/stages/generalization.rs b/libafl/src/stages/generalization.rs
index d8e389227c..0e94d8338e 100644
--- a/libafl/src/stages/generalization.rs
+++ b/libafl/src/stages/generalization.rs
@@ -13,7 +13,7 @@ use serde::{Deserialize, Serialize};
 use crate::monitors::PerfFeature;
 use crate::{
     bolts::AsSlice,
-    corpus::Corpus,
+    corpus::{Corpus, CorpusId},
     executors::{Executor, HasObservers},
     feedbacks::map::MapNoveltiesMetadata,
     inputs::{GeneralizedInput, GeneralizedItem, HasBytesVec, UsesInput},
@@ -31,7 +31,7 @@ const MAX_GENERALIZED_LEN: usize = 8192;
 #[derive(Debug, Default, Serialize, Deserialize)]
 pub struct GeneralizedIndexesMetadata {
     /// The set of indexes
-    pub indexes: HashSet<usize>,
+    pub indexes: HashSet<CorpusId>,
 }
 
 crate::impl_serdeany!(GeneralizedIndexesMetadata);
@@ -95,7 +95,7 @@ where
         executor: &mut E,
         state: &mut E::State,
         manager: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         if state
             .metadata()
diff --git a/libafl/src/stages/mod.rs b/libafl/src/stages/mod.rs
index ab50cef54f..f05b8443f7 100644
--- a/libafl/src/stages/mod.rs
+++ b/libafl/src/stages/mod.rs
@@ -54,6 +54,7 @@ pub use dump::*;
 
 use self::push::PushStage;
 use crate::{
+    corpus::CorpusId,
     events::{EventFirer, EventRestarter, HasEventManagerId, ProgressReporter},
     executors::{Executor, HasObservers},
     inputs::UsesInput,
@@ -78,7 +79,7 @@ where
         executor: &mut E,
         state: &mut Self::State,
         manager: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error>;
 }
 
@@ -97,7 +98,7 @@ where
         executor: &mut E,
         state: &mut S,
         manager: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error>;
 }
 
@@ -114,7 +115,7 @@ where
         _: &mut E,
         _: &mut S,
         _: &mut EM,
-        _: usize,
+        _: CorpusId,
     ) -> Result<(), Error> {
         Ok(())
     }
@@ -134,7 +135,7 @@ where
         executor: &mut E,
         state: &mut Head::State,
         manager: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         // Perform the current stage
         self.0
@@ -150,7 +151,7 @@ where
 #[derive(Debug)]
 pub struct ClosureStage<CB, E, EM, Z>
 where
-    CB: FnMut(&mut Z, &mut E, &mut E::State, &mut EM, usize) -> Result<(), Error>,
+    CB: FnMut(&mut Z, &mut E, &mut E::State, &mut EM, CorpusId) -> Result<(), Error>,
     E: UsesState,
 {
     closure: CB,
@@ -159,7 +160,7 @@ where
 
 impl<CB, E, EM, Z> UsesState for ClosureStage<CB, E, EM, Z>
 where
-    CB: FnMut(&mut Z, &mut E, &mut E::State, &mut EM, usize) -> Result<(), Error>,
+    CB: FnMut(&mut Z, &mut E, &mut E::State, &mut EM, CorpusId) -> Result<(), Error>,
     E: UsesState,
 {
     type State = E::State;
@@ -167,7 +168,7 @@ where
 
 impl<CB, E, EM, Z> Stage<E, EM, Z> for ClosureStage<CB, E, EM, Z>
 where
-    CB: FnMut(&mut Z, &mut E, &mut E::State, &mut EM, usize) -> Result<(), Error>,
+    CB: FnMut(&mut Z, &mut E, &mut E::State, &mut EM, CorpusId) -> Result<(), Error>,
     E: UsesState,
     EM: UsesState<State = E::State>,
     Z: UsesState<State = E::State>,
@@ -178,7 +179,7 @@ where
         executor: &mut E,
         state: &mut E::State,
         manager: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         (self.closure)(fuzzer, executor, state, manager, corpus_idx)
     }
@@ -187,7 +188,7 @@ where
 /// A stage that takes a closure
 impl<CB, E, EM, Z> ClosureStage<CB, E, EM, Z>
 where
-    CB: FnMut(&mut Z, &mut E, &mut E::State, &mut EM, usize) -> Result<(), Error>,
+    CB: FnMut(&mut Z, &mut E, &mut E::State, &mut EM, CorpusId) -> Result<(), Error>,
     E: UsesState,
 {
     /// Create a new [`ClosureStage`]
@@ -202,7 +203,7 @@ where
 
 impl<CB, E, EM, Z> From<CB> for ClosureStage<CB, E, EM, Z>
 where
-    CB: FnMut(&mut Z, &mut E, &mut E::State, &mut EM, usize) -> Result<(), Error>,
+    CB: FnMut(&mut Z, &mut E, &mut E::State, &mut EM, CorpusId) -> Result<(), Error>,
     E: UsesState,
 {
     #[must_use]
@@ -260,7 +261,7 @@ where
         executor: &mut E,
         state: &mut CS::State,
         event_mgr: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         let push_stage = &mut self.push_stage;
 
@@ -365,7 +366,7 @@ where
         executor: &mut E,
         state: &mut ST::State,
         manager: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         let condition = &mut self.condition;
         if condition(state) == SkippableStageDecision::Perform {
@@ -386,6 +387,7 @@ pub mod pybind {
     use pyo3::prelude::*;
 
     use crate::{
+        corpus::CorpusId,
         events::pybind::PythonEventManager,
         executors::pybind::PythonExecutor,
         fuzzer::pybind::{PythonStdFuzzer, PythonStdFuzzerWrapper},
@@ -421,7 +423,7 @@ pub mod pybind {
             executor: &mut PythonExecutor,
             state: &mut PythonStdState,
             manager: &mut PythonEventManager,
-            corpus_idx: usize,
+            corpus_idx: CorpusId,
         ) -> Result<(), Error> {
             Python::with_gil(|py| -> PyResult<()> {
                 self.inner.call_method1(
@@ -432,7 +434,7 @@ pub mod pybind {
                         executor.clone(),
                         PythonStdStateWrapper::wrap(state),
                         manager.clone(),
-                        corpus_idx,
+                        corpus_idx.0,
                     ),
                 )?;
                 Ok(())
@@ -510,7 +512,7 @@ pub mod pybind {
             executor: &mut PythonExecutor,
             state: &mut PythonStdState,
             manager: &mut PythonEventManager,
-            corpus_idx: usize,
+            corpus_idx: CorpusId,
         ) -> Result<(), Error> {
             unwrap_me_mut!(self.wrapper, s, {
                 s.perform(fuzzer, executor, state, manager, corpus_idx)
@@ -549,7 +551,7 @@ pub mod pybind {
             executor: &mut PythonExecutor,
             state: &mut PythonStdState,
             manager: &mut PythonEventManager,
-            corpus_idx: usize,
+            corpus_idx: CorpusId,
         ) -> Result<(), Error> {
             for s in &mut self.list {
                 s.perform(fuzzer, executor, state, manager, corpus_idx)?;
diff --git a/libafl/src/stages/mutational.rs b/libafl/src/stages/mutational.rs
index 57a2ae6e7f..016d3626cb 100644
--- a/libafl/src/stages/mutational.rs
+++ b/libafl/src/stages/mutational.rs
@@ -7,7 +7,7 @@ use core::marker::PhantomData;
 use crate::monitors::PerfFeature;
 use crate::{
     bolts::rands::Rand,
-    corpus::Corpus,
+    corpus::{Corpus, CorpusId},
     fuzzer::Evaluator,
     mark_feature_time,
     mutators::Mutator,
@@ -37,7 +37,7 @@ where
     fn mutator_mut(&mut self) -> &mut M;
 
     /// Gets the number of iterations this mutator should run for.
-    fn iterations(&self, state: &mut Z::State, corpus_idx: usize) -> Result<u64, Error>;
+    fn iterations(&self, state: &mut Z::State, corpus_idx: CorpusId) -> Result<u64, Error>;
 
     /// Runs this (mutational) stage for the given testcase
     #[allow(clippy::cast_possible_wrap)] // more than i32 stages on 32 bit system - highly unlikely...
@@ -47,7 +47,7 @@ where
         executor: &mut E,
         state: &mut Z::State,
         manager: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         let num = self.iterations(state, corpus_idx)?;
 
@@ -109,7 +109,7 @@ where
     }
 
     /// Gets the number of iterations as a random number
-    fn iterations(&self, state: &mut Z::State, _corpus_idx: usize) -> Result<u64, Error> {
+    fn iterations(&self, state: &mut Z::State, _corpus_idx: CorpusId) -> Result<u64, Error> {
         Ok(1 + state.rand_mut().below(DEFAULT_MUTATIONAL_MAX_ITERATIONS))
     }
 }
@@ -141,7 +141,7 @@ where
         executor: &mut E,
         state: &mut Z::State,
         manager: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         let ret = self.perform_mutational(fuzzer, executor, state, manager, corpus_idx);
 
diff --git a/libafl/src/stages/owned.rs b/libafl/src/stages/owned.rs
index 11e335bf1c..5983234b55 100644
--- a/libafl/src/stages/owned.rs
+++ b/libafl/src/stages/owned.rs
@@ -4,6 +4,7 @@ use alloc::{boxed::Box, vec::Vec};
 
 use crate::{
     bolts::anymap::AsAny,
+    corpus::CorpusId,
     stages::{Stage, StagesTuple},
     state::UsesState,
     Error,
@@ -42,7 +43,7 @@ where
         executor: &mut E,
         state: &mut E::State,
         manager: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         for s in &mut self.list {
             s.perform(fuzzer, executor, state, manager, corpus_idx)?;
diff --git a/libafl/src/stages/power.rs b/libafl/src/stages/power.rs
index e94bb208e5..70719cfa31 100644
--- a/libafl/src/stages/power.rs
+++ b/libafl/src/stages/power.rs
@@ -5,7 +5,7 @@ use core::{fmt::Debug, marker::PhantomData};
 
 use crate::{
     bolts::tuples::MatchName,
-    corpus::{Corpus, SchedulerTestcaseMetaData},
+    corpus::{Corpus, CorpusId, SchedulerTestcaseMetaData},
     executors::{Executor, HasObservers},
     fuzzer::Evaluator,
     mutators::Mutator,
@@ -58,7 +58,7 @@ where
 
     /// Gets the number of iterations as a random number
     #[allow(clippy::cast_sign_loss)]
-    fn iterations(&self, state: &mut E::State, corpus_idx: usize) -> Result<u64, Error> {
+    fn iterations(&self, state: &mut E::State, corpus_idx: CorpusId) -> Result<u64, Error> {
         // Update handicap
         let mut testcase = state.corpus().get(corpus_idx)?.borrow_mut();
         let score = F::compute(&mut *testcase, state)? as u64;
@@ -73,7 +73,7 @@ where
         executor: &mut E,
         state: &mut E::State,
         manager: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         let num = self.iterations(state, corpus_idx)?;
 
@@ -143,7 +143,7 @@ where
         executor: &mut E,
         state: &mut E::State,
         manager: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         let ret = self.perform_mutational(fuzzer, executor, state, manager, corpus_idx);
         ret
diff --git a/libafl/src/stages/push/mod.rs b/libafl/src/stages/push/mod.rs
index 71ed01a0b2..bb0ce56030 100644
--- a/libafl/src/stages/push/mod.rs
+++ b/libafl/src/stages/push/mod.rs
@@ -17,6 +17,7 @@ pub use mutational::StdMutationalPushStage;
 
 use crate::{
     bolts::current_time,
+    corpus::CorpusId,
     events::{EventFirer, EventRestarter, HasEventManagerId, ProgressReporter},
     executors::ExitKind,
     inputs::UsesInput,
@@ -100,7 +101,7 @@ where
     pub errored: bool,
 
     /// The corpus index we're currently working on
-    pub current_corpus_idx: Option<usize>,
+    pub current_corpus_idx: Option<CorpusId>,
 
     /// The input we just ran
     pub current_input: Option<<CS::State as UsesInput>::Input>, // Todo: Get rid of copy
@@ -196,7 +197,7 @@ where
     fn push_stage_helper_mut(&mut self) -> &mut PushStageHelper<CS, EM, OT, Z>;
 
     /// Set the current corpus index this stage works on
-    fn set_current_corpus_idx(&mut self, corpus_idx: usize) {
+    fn set_current_corpus_idx(&mut self, corpus_idx: CorpusId) {
         self.push_stage_helper_mut().current_corpus_idx = Some(corpus_idx);
     }
 
diff --git a/libafl/src/stages/push/mutational.rs b/libafl/src/stages/push/mutational.rs
index 92c0dded2e..a0b6d8f7d9 100644
--- a/libafl/src/stages/push/mutational.rs
+++ b/libafl/src/stages/push/mutational.rs
@@ -12,7 +12,7 @@ use super::{PushStage, PushStageHelper, PushStageSharedState};
 use crate::monitors::PerfFeature;
 use crate::{
     bolts::rands::Rand,
-    corpus::Corpus,
+    corpus::{Corpus, CorpusId},
     events::{EventFirer, EventRestarter, HasEventManagerId, ProgressReporter},
     executors::ExitKind,
     inputs::UsesInput,
@@ -48,7 +48,7 @@ where
         + EvaluatorObservers<OT>
         + HasScheduler<Scheduler = CS>,
 {
-    current_corpus_idx: Option<usize>,
+    current_corpus_idx: Option<CorpusId>,
     testcases_to_do: usize,
     testcases_done: usize,
 
@@ -72,12 +72,12 @@ where
 {
     /// Gets the number of iterations as a random number
     #[allow(clippy::unused_self, clippy::unnecessary_wraps)] // TODO: we should put this function into a trait later
-    fn iterations(&self, state: &mut CS::State, _corpus_idx: usize) -> Result<usize, Error> {
+    fn iterations(&self, state: &mut CS::State, _corpus_idx: CorpusId) -> Result<usize, Error> {
         Ok(1 + state.rand_mut().below(DEFAULT_MUTATIONAL_MAX_ITERATIONS) as usize)
     }
 
     /// Sets the current corpus index
-    pub fn set_current_corpus_idx(&mut self, current_corpus_idx: usize) {
+    pub fn set_current_corpus_idx(&mut self, current_corpus_idx: CorpusId) {
         self.current_corpus_idx = Some(current_corpus_idx);
     }
 }
@@ -175,7 +175,7 @@ where
 
         start_timer!(state);
         self.mutator
-            .post_exec(state, self.stage_idx, Some(self.testcases_done))?;
+            .post_exec(state, self.stage_idx, self.current_corpus_idx)?;
         mark_feature_time!(state, PerfFeature::MutatePostExec);
         self.testcases_done += 1;
 
diff --git a/libafl/src/stages/sync.rs b/libafl/src/stages/sync.rs
index 10ac9853a9..1d6ff49d95 100644
--- a/libafl/src/stages/sync.rs
+++ b/libafl/src/stages/sync.rs
@@ -10,6 +10,7 @@ use std::{
 use serde::{Deserialize, Serialize};
 
 use crate::{
+    corpus::CorpusId,
     fuzzer::Evaluator,
     inputs::{Input, UsesInput},
     stages::Stage,
@@ -64,7 +65,7 @@ where
         executor: &mut E,
         state: &mut Z::State,
         manager: &mut EM,
-        _corpus_idx: usize,
+        _corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         let last = state
             .metadata()
diff --git a/libafl/src/stages/tmin.rs b/libafl/src/stages/tmin.rs
index 0e956b2ecb..e3faa7826e 100644
--- a/libafl/src/stages/tmin.rs
+++ b/libafl/src/stages/tmin.rs
@@ -13,7 +13,7 @@ use ahash::AHasher;
 use crate::monitors::PerfFeature;
 use crate::{
     bolts::{tuples::Named, HasLen},
-    corpus::{Corpus, Testcase},
+    corpus::{Corpus, CorpusId, Testcase},
     events::EventFirer,
     executors::{Executor, ExitKind, HasObservers},
     feedbacks::{Feedback, FeedbackFactory, HasObserverName},
@@ -55,7 +55,7 @@ where
     fn mutator_mut(&mut self) -> &mut M;
 
     /// Gets the number of iterations this mutator should run for.
-    fn iterations(&self, state: &mut CS::State, corpus_idx: usize) -> Result<usize, Error>;
+    fn iterations(&self, state: &mut CS::State, corpus_idx: CorpusId) -> Result<usize, Error>;
 
     /// Runs this (mutational) stage for new objectives
     #[allow(clippy::cast_possible_wrap)] // more than i32 stages on 32 bit system - highly unlikely...
@@ -65,7 +65,7 @@ where
         executor: &mut E,
         state: &mut CS::State,
         manager: &mut EM,
-        base_corpus_idx: usize,
+        base_corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         let orig_max_size = state.max_size();
         // basically copy-pasted from mutational.rs
@@ -207,7 +207,7 @@ where
         executor: &mut E,
         state: &mut CS::State,
         manager: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         self.perform_minification(fuzzer, executor, state, manager, corpus_idx)?;
 
@@ -262,7 +262,7 @@ where
     }
 
     /// Gets the number of iterations from a fixed number of runs
-    fn iterations(&self, _state: &mut CS::State, _corpus_idx: usize) -> Result<usize, Error> {
+    fn iterations(&self, _state: &mut CS::State, _corpus_idx: CorpusId) -> Result<usize, Error> {
         Ok(self.runs)
     }
 }
diff --git a/libafl/src/stages/tracing.rs b/libafl/src/stages/tracing.rs
index 725354048d..af5fcf4480 100644
--- a/libafl/src/stages/tracing.rs
+++ b/libafl/src/stages/tracing.rs
@@ -5,7 +5,7 @@ use core::{fmt::Debug, marker::PhantomData};
 #[cfg(feature = "introspection")]
 use crate::monitors::PerfFeature;
 use crate::{
-    corpus::Corpus,
+    corpus::{Corpus, CorpusId},
     executors::{Executor, HasObservers, ShadowExecutor},
     mark_feature_time,
     observers::ObserversTuple,
@@ -45,7 +45,7 @@ where
         _executor: &mut E,
         state: &mut TE::State,
         manager: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         start_timer!(state);
         let input = state
@@ -124,7 +124,7 @@ where
         executor: &mut ShadowExecutor<E, SOT>,
         state: &mut E::State,
         manager: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         start_timer!(state);
         let input = state
diff --git a/libafl/src/stages/tuneable.rs b/libafl/src/stages/tuneable.rs
index ff68fea670..efdce30084 100644
--- a/libafl/src/stages/tuneable.rs
+++ b/libafl/src/stages/tuneable.rs
@@ -6,6 +6,7 @@ use serde::{Deserialize, Serialize};
 
 use crate::{
     bolts::rands::Rand,
+    corpus::CorpusId,
     impl_serdeany,
     mutators::Mutator,
     stages::{mutational::DEFAULT_MUTATIONAL_MAX_ITERATIONS, MutationalStage, Stage},
@@ -78,7 +79,7 @@ where
 
     /// Gets the number of iterations as a random number
     #[allow(clippy::cast_possible_truncation)]
-    fn iterations(&self, state: &mut Z::State, _corpus_idx: usize) -> Result<u64, Error> {
+    fn iterations(&self, state: &mut Z::State, _corpus_idx: CorpusId) -> Result<u64, Error> {
         Ok(if let Some(iters) = get_iters(state)? {
             iters
         } else {
@@ -115,7 +116,7 @@ where
         executor: &mut E,
         state: &mut Z::State,
         manager: &mut EM,
-        corpus_idx: usize,
+        corpus_idx: CorpusId,
     ) -> Result<(), Error> {
         let ret = self.perform_mutational(fuzzer, executor, state, manager, corpus_idx);