diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 3ac5d8eb4..a0c26bf59 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -82,7 +82,7 @@
         - [`get_bitfield_bit`](#get_bitfield_bit)
         - [`verify_bitfield`](#verify_bitfield)
         - [`convert_to_indexed`](#convert_to_indexed)
-        - [`verify_indexed_attestation`](#verify_indexed_attestation)
+        - [`validate_indexed_attestation`](#validate_indexed_attestation)
         - [`is_slashable_attestation_data`](#is_slashable_attestation_data)
         - [`integer_squareroot`](#integer_squareroot)
         - [`get_delayed_activation_exit_epoch`](#get_delayed_activation_exit_epoch)
@@ -1019,35 +1019,29 @@ def convert_to_indexed(state: BeaconState, attestation: Attestation) -> IndexedA
     )
 ```
 
-### `verify_indexed_attestation`
+### `validate_indexed_attestation`
 
 ```python
-def verify_indexed_attestation(state: BeaconState, indexed_attestation: IndexedAttestation) -> bool:
+def validate_indexed_attestation(state: BeaconState, indexed_attestation: IndexedAttestation) -> None:
     """
-    Verify validity of ``indexed_attestation`` fields.
+    Verify validity of ``indexed_attestation``.
     """
-    custody_bit_0_indices = indexed_attestation.custody_bit_0_indices
-    custody_bit_1_indices = indexed_attestation.custody_bit_1_indices
+    bit_0_indices = indexed_attestation.custody_bit_0_indices
+    bit_1_indices = indexed_attestation.custody_bit_1_indices
 
-    # Ensure no duplicate indices across custody bits
-    assert len(set(custody_bit_0_indices).intersection(set(custody_bit_1_indices))) == 0
-
-    if len(custody_bit_1_indices) > 0:  # [TO BE REMOVED IN PHASE 1]
-        return False
-
-    if not (1 <= len(custody_bit_0_indices) + len(custody_bit_1_indices) <= MAX_INDICES_PER_ATTESTATION):
-        return False
-
-    if custody_bit_0_indices != sorted(custody_bit_0_indices):
-        return False
-
-    if custody_bit_1_indices != sorted(custody_bit_1_indices):
-        return False
-
-    return bls_verify_multiple(
+    # Verify no index has custody bit equal to 1 [to be removed in phase 1]
+    assert len(bit_1_indices) == 0
+    # Verify max number of indices
+    assert len(bit_0_indices) + len(bit_1_indices) <= MAX_INDICES_PER_ATTESTATION
+    # Verify index sets are disjoint
+    assert len(set(bit_0_indices).intersection(bit_1_indices)) == 0
+    # Verify indices are sorted
+    assert bit_0_indices == sorted(bit_0_indices) and bit_1_indices == sorted(bit_1_indices)
+    # Verify aggregate signature
+    assert bls_verify_multiple(
         pubkeys=[
-            bls_aggregate_pubkeys([state.validator_registry[i].pubkey for i in custody_bit_0_indices]),
-            bls_aggregate_pubkeys([state.validator_registry[i].pubkey for i in custody_bit_1_indices]),
+            bls_aggregate_pubkeys([state.validator_registry[i].pubkey for i in bit_0_indices]),
+            bls_aggregate_pubkeys([state.validator_registry[i].pubkey for i in bit_1_indices]),
         ],
         message_hashes=[
             hash_tree_root(AttestationDataAndCustodyBit(data=indexed_attestation.data, custody_bit=0b0)),
@@ -1672,8 +1666,8 @@ def process_attester_slashing(state: BeaconState,
     attestation_1 = attester_slashing.attestation_1
     attestation_2 = attester_slashing.attestation_2
     assert is_slashable_attestation_data(attestation_1.data, attestation_2.data)
-    assert verify_indexed_attestation(state, attestation_1)
-    assert verify_indexed_attestation(state, attestation_2)
+    validate_indexed_attestation(state, attestation_1)
+    validate_indexed_attestation(state, attestation_2)
 
     slashed_any = False
     attesting_indices_1 = attestation_1.custody_bit_0_indices + attestation_1.custody_bit_1_indices
@@ -1722,7 +1716,7 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
     assert data.crosslink.epoch == min(data.target_epoch, parent_crosslink.epoch + MAX_EPOCHS_PER_CROSSLINK)
     assert data.crosslink.parent_root == hash_tree_root(parent_crosslink)
     assert data.crosslink.data_root == ZERO_HASH  # [to be removed in phase 1]
-    assert verify_indexed_attestation(state, convert_to_indexed(state, attestation))
+    validate_indexed_attestation(state, convert_to_indexed(state, attestation))
 ```
 
 ##### Deposits
diff --git a/test_libs/pyspec/tests/block_processing/test_process_attestation.py b/test_libs/pyspec/tests/block_processing/test_process_attestation.py
index fcbc68fe9..9cf08bae2 100644
--- a/test_libs/pyspec/tests/block_processing/test_process_attestation.py
+++ b/test_libs/pyspec/tests/block_processing/test_process_attestation.py
@@ -150,6 +150,6 @@ def test_empty_aggregation_bitfield(state):
 
     attestation.aggregation_bitfield = b'\x00' * len(attestation.aggregation_bitfield)
 
-    pre_state, post_state = run_attestation_processing(state, attestation, False)
+    pre_state, post_state = run_attestation_processing(state, attestation)
 
     return pre_state, attestation, post_state