diff --git a/helper_functions/src/error.rs b/helper_functions/src/error.rs
index dfe4958c..c7abe1e1 100644
--- a/helper_functions/src/error.rs
+++ b/helper_functions/src/error.rs
@@ -11,8 +11,11 @@ pub(crate) enum Error {
     AttestingIndicesNotSortedAndUnique,
     #[error("commitee index is out of bounds")]
     CommitteeIndexOutOfBounds,
-    #[error("aggregation bitlist length does not match committee length")]
-    CommitteeLengthMismatch,
+    #[error("aggregation bitlist length {aggregation_bitlist_length} does not match committee length {committee_length}")]
+    CommitteeLengthMismatch {
+        aggregation_bitlist_length: usize,
+        committee_length: usize,
+    },
     #[error("epoch is after next one relative to state")]
     EpochAfterNext,
     #[error("epoch is before previous one relative to state")]
diff --git a/helper_functions/src/phase0.rs b/helper_functions/src/phase0.rs
index ab64c9a1..c86a1dd7 100644
--- a/helper_functions/src/phase0.rs
+++ b/helper_functions/src/phase0.rs
@@ -54,7 +54,10 @@ pub fn get_attesting_indices<'all, P: Preset>(
 
     ensure!(
         committee.len() == aggregation_bits.len(),
-        Error::CommitteeLengthMismatch,
+        Error::CommitteeLengthMismatch {
+            aggregation_bitlist_length: aggregation_bits.len(),
+            committee_length: committee.len(),
+        },
     );
 
     // `Itertools::zip_eq` is slower than `Iterator::zip` when iterating over packed indices.