diff --git a/beacon_chain/validation/src/attestation_validation.rs b/beacon_chain/validation/src/attestation_validation.rs
index 4953a92c3..5d45bfcd2 100644
--- a/beacon_chain/validation/src/attestation_validation.rs
+++ b/beacon_chain/validation/src/attestation_validation.rs
@@ -135,7 +135,7 @@ where
          * Allow extra set bits would permit mutliple different byte layouts (and therefore hashes) to
          * refer to the same AttesationRecord.
          */
-        if a.attester_bitfield.len() > attestation_indices.len() {
+        if a.attester_bitfield.num_set_bits() > attestation_indices.len() {
             return Err(AttestationValidationError::InvalidBitfieldEndBits);
         }