diff --git a/scripts/build_spec.py b/scripts/build_spec.py
index 0a41fe5c0..1f5fe1ee6 100644
--- a/scripts/build_spec.py
+++ b/scripts/build_spec.py
@@ -25,7 +25,7 @@ from eth2spec.utils.ssz.ssz_impl import (
     signing_root,
 )
 from eth2spec.utils.ssz.ssz_typing import (
-    bit, boolean, Container, List, Vector, Bytes, uint64,
+    bit, boolean, Container, List, Vector, uint64,
     Bytes4, Bytes32, Bytes48, Bytes96, Bitlist, Bitvector,
 )
 from eth2spec.utils.bls import (
diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 4d3fe9773..f596da520 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -1292,7 +1292,8 @@ def process_justification_and_finalization(state: BeaconState) -> None:
     # Process justifications
     state.previous_justified_epoch = state.current_justified_epoch
     state.previous_justified_root = state.current_justified_root
-    state.justification_bitfield = Bitvector[4](*([0b0] + state.justification_bitfield[0:JUSTIFICATION_BITVECTOR_LENGTH - 1]))
+    state.justification_bitfield = Bitvector[JUSTIFICATION_BITVECTOR_LENGTH](
+        *([0b0] + state.justification_bitfield[0:JUSTIFICATION_BITVECTOR_LENGTH - 1]))
     previous_epoch_matching_target_balance = get_attesting_balance(
         state, get_matching_target_attestations(state, previous_epoch)
     )
diff --git a/specs/core/1_custody-game.md b/specs/core/1_custody-game.md
index 17f599fcd..9ad00516e 100644
--- a/specs/core/1_custody-game.md
+++ b/specs/core/1_custody-game.md
@@ -574,7 +574,6 @@ def process_bit_challenge(state: BeaconState,
 
     # Verify the chunk count
     chunk_count = get_custody_chunk_count(attestation.data.crosslink)
-    assert verify_bitfield(challenge.chunk_bits, chunk_count)
     # Verify the first bit of the hash of the chunk bits does not equal the custody bit
     custody_bit = attestation.custody_bitfield[attesters.index(challenge.responder_index)]
     assert custody_bit != get_bitfield_bit(get_chunk_bits_root(challenge.chunk_bits), 0)