diff --git a/libafl_targets/src/libfuzzer/mutators.rs b/libafl_targets/src/libfuzzer/mutators.rs
index a57b7fa751..7511766823 100644
--- a/libafl_targets/src/libfuzzer/mutators.rs
+++ b/libafl_targets/src/libfuzzer/mutators.rs
@@ -350,7 +350,7 @@ where
             return result.replace(Ok(MutationResult::Skipped));
         }
         if new_len > len_max {
-            return Err(Error::illegal_state("LLVMFuzzerCustomMutator returned more bytes than allowed. Expected up to {max_len} but got {new_len}"));
+            return Err(Error::illegal_state(format!("LLVMFuzzerCustomMutator returned more bytes than allowed. Expected up to {max_len} but got {new_len}")));
         }
         input.resize(new_len, 0);
         Ok(MutationResult::Mutated)
@@ -448,7 +448,7 @@ where
         }
 
         if new_len > len_max {
-            return Err(Error::illegal_state("LLVMFuzzerCustomCrossOver returned more bytes than allowed. Expected up to {max_len} but got {new_len}"));
+            return Err(Error::illegal_state(format!("LLVMFuzzerCustomCrossOver returned more bytes than allowed. Expected up to {max_len} but got {new_len}")));
         }
 
         input.resize(new_len, 0);