diff --git a/utils/runtime-fuzzer/src/gear_calls.rs b/utils/runtime-fuzzer/src/gear_calls.rs
index 568a2fda68f..8607a335033 100644
--- a/utils/runtime-fuzzer/src/gear_calls.rs
+++ b/utils/runtime-fuzzer/src/gear_calls.rs
@@ -54,6 +54,9 @@ static_assertions::const_assert!(MAX_SALT_SIZE <= gear_core::message::MAX_PAYLOA
 
 const ID_SIZE: usize = mem::size_of::<ProgramId>();
 const GAS_AND_VALUE_SIZE: usize = mem::size_of::<(u64, u128)>();
+// Used to make sure that generators will not exceed `Unstructured` size as it's used not only
+// to generate things like wasm code or message payload but also to generate some auxiliary
+// data, for example index in some vec.
 const AUXILIARY_SIZE: usize = 512;
 
 /// This trait provides ability for [`ExtrinsicGenerator`]s to fetch messages