diff --git a/shared/attestationutil/attestation_utils.go b/shared/attestationutil/attestation_utils.go
index 5f39f24ff..7caf9f0b6 100644
--- a/shared/attestationutil/attestation_utils.go
+++ b/shared/attestationutil/attestation_utils.go
@@ -67,7 +67,7 @@ func ConvertToIndexed(ctx context.Context, attestation *ethpb.Attestation, commi
 //    committee = get_beacon_committee(state, data.slot, data.index)
 //    return set(index for i, index in enumerate(committee) if bits[i])
 func AttestingIndices(bf bitfield.Bitfield, committee []uint64) []uint64 {
-	indices := make([]uint64, 0, len(committee))
+	indices := make([]uint64, 0, bf.Count())
 	for _, idx := range bf.BitIndices() {
 		if idx < len(committee) {
 			indices = append(indices, committee[idx])
diff --git a/shared/attestationutil/attestation_utils_test.go b/shared/attestationutil/attestation_utils_test.go
index de07ca61c..6ba75b14b 100644
--- a/shared/attestationutil/attestation_utils_test.go
+++ b/shared/attestationutil/attestation_utils_test.go
@@ -114,9 +114,10 @@ func TestIsValidAttestationIndices(t *testing.T) {
 }
 
 func BenchmarkAttestingIndices_PartialCommittee(b *testing.B) {
-	bf := bitfield.Bitlist{0b11111111, 0b11111111, 0b11111111, 0b11111111, 0b100}
+	bf := bitfield.Bitlist{0b11111111, 0b11111111, 0b10000111, 0b11111111, 0b100}
 	committee := []uint64{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34}
 
+	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		_ = attestationutil.AttestingIndices(bf, committee)
 	}