diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 71ad5c708..1c5af9660 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -1631,9 +1631,12 @@ For each `attestation` in `block.body.attestations`:
 ```python
     assert attestation.custody_bitfield == b'\x00' * len(attestation.custody_bitfield)  # [TO BE REMOVED IN PHASE 1]
     assert attestation.aggregation_bitfield != b'\x00' * len(attestation.aggregation_bitfield)
-
-    assert len(attestation.aggregation_bitfield) <= len(attestation.custody_bitfield)
-    for i in range(len(attestation.aggregation_bitfield)):
+    
+    crosslink_committee = get_crosslink_committee_at_slot(state, attestation.data.slot)[0]
+    verify_bitfield(attestation.aggregation_bitfield, len(crosslink_committee))
+    verify_bitfield(attestation.custody_bitfield, len(crosslink_committee))
+    
+    for i in range(len(crosslink_committee):
         if get_bitfield_bit(attestation.aggregation_bitfield, i) == 0b0:
             assert get_bitfield_bit(attestation.custody_bitfield, i) == 0b0