diff --git a/fuzzers/FRET/src/fuzzer.rs b/fuzzers/FRET/src/fuzzer.rs
index 365adae756..b9e59a3342 100644
--- a/fuzzers/FRET/src/fuzzer.rs
+++ b/fuzzers/FRET/src/fuzzer.rs
@@ -377,6 +377,7 @@ let denylist=isr_ranges.values().map(|x| x.clone()).collect();
 let denylist = QemuInstrumentationFilter::DenyList(denylist); // do not count isr jumps, which are useless
 #[cfg(feature = "observe_systemstate")]
 let mut isr_addreses : HashMap<GuestAddr, String> = systemstate::helpers::ISR_SYMBOLS.iter().filter_map(|x| (api_ranges.remove(&x.to_string()).map(|y| (y.start,x.to_string())))).collect();
+#[cfg(feature = "observe_systemstate")]
 systemstate::helpers::ISR_SYMBOLS.iter().for_each(|x| {let _ =(app_fn_ranges.get(&x.to_string()).map(|y| (x.to_string(),y.clone()))).map(|y| isr_addreses.insert(y.1.start, y.0));});    // add used defined isr
 
 #[cfg(feature = "observe_systemstate")]