diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index 6e8700e2f..8c7af6c4f 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -54,7 +54,6 @@
     - [`get_shard_proposer_index`](#get_shard_proposer_index)
     - [`get_committee_count_delta`](#get_committee_count_delta)
     - [`get_start_shard`](#get_start_shard)
-    - [`get_shard`](#get_shard)
     - [`get_latest_slot_for_shard`](#get_latest_slot_for_shard)
     - [`get_offset_slots`](#get_offset_slots)
   - [Predicates](#predicates)
@@ -167,6 +166,8 @@ class AttestationData(Container):
     # FFG vote
     source: Checkpoint
     target: Checkpoint
+    # Shard vote
+    shard: Shard
     # Current-slot shard block root
     shard_head_root: Root
     # Shard transition root
@@ -621,16 +622,6 @@ def get_start_shard(state: BeaconState, slot: Slot) -> Shard:
         )
 ```
 
-#### `get_shard`
-
-```python
-def get_shard(state: BeaconState, attestation: Attestation) -> Shard:
-    """
-    Return the shard that the given ``attestation`` is attesting.
-    """
-    return compute_shard_from_committee_index(state, attestation.data.index, attestation.data.slot)
-```
-
 #### `get_latest_slot_for_shard`
 
 ```python
@@ -775,6 +766,9 @@ def validate_attestation(state: BeaconState, attestation: Attestation) -> None:
     if is_on_time_attestation(state, attestation):
         # Correct parent block root
         assert data.beacon_block_root == get_block_root_at_slot(state, compute_previous_slot(state.slot))
+        # Correct shard number
+        shard = compute_shard_from_committee_index(state, attestation.data.index, attestation.data.slot)
+        assert attestation.data.shard == shard
     # Type 2: no shard transition
     else:
         # Ensure delayed attestation
@@ -879,7 +873,6 @@ def process_crosslink_for_shard(state: BeaconState,
     on_time_attestation_slot = compute_previous_slot(state.slot)
     committee = get_beacon_committee(state, on_time_attestation_slot, committee_index)
     online_indices = get_online_validator_indices(state)
-    shard = compute_shard_from_committee_index(state, committee_index, on_time_attestation_slot)
 
     # Loop over all shard transition roots
     shard_transition_roots = set([a.data.shard_transition_root for a in attestations])
@@ -905,7 +898,7 @@ def process_crosslink_for_shard(state: BeaconState,
         assert shard_transition_root == hash_tree_root(shard_transition)
 
         # Apply transition
-        apply_shard_transition(state, shard, shard_transition)
+        apply_shard_transition(state, attestation.data.shard, shard_transition)
         # Apply proposer reward and cost
         beacon_proposer_index = get_beacon_proposer_index(state)
         estimated_attester_reward = sum([get_base_reward(state, attester) for attester in transition_participants])
@@ -913,11 +906,11 @@ def process_crosslink_for_shard(state: BeaconState,
         increase_balance(state, beacon_proposer_index, proposer_reward)
         states_slots_lengths = zip(
             shard_transition.shard_states,
-            get_offset_slots(state, shard),
+            get_offset_slots(state, attestation.data.shard),
             shard_transition.shard_block_lengths
         )
         for shard_state, slot, length in states_slots_lengths:
-            proposer_index = get_shard_proposer_index(state, slot, shard)
+            proposer_index = get_shard_proposer_index(state, slot, attestation.data.shard)
             decrease_balance(state, proposer_index, shard_state.gasprice * length)
 
         # Return winning transition root
@@ -938,12 +931,15 @@ def process_crosslinks(state: BeaconState,
     committee_count = get_committee_count_at_slot(state, on_time_attestation_slot)
     for committee_index in map(CommitteeIndex, range(committee_count)):
         # All attestations in the block for this committee/shard and current slot
+        shard = compute_shard_from_committee_index(state, committee_index, on_time_attestation_slot)
+        # Since the attestations are validated, all `shard_attestations` satisfy `attestation.data.shard == shard`
         shard_attestations = [
             attestation for attestation in attestations
             if is_on_time_attestation(state, attestation) and attestation.data.index == committee_index
         ]
-        shard = compute_shard_from_committee_index(state, committee_index, on_time_attestation_slot)
-        winning_root = process_crosslink_for_shard(state, committee_index, shard_transitions[shard], shard_attestations)
+        winning_root = process_crosslink_for_shard(
+            state, committee_index, shard_transitions[shard], shard_attestations
+        )
         if winning_root != Root():
             # Mark relevant pending attestations as creating a successful crosslink
             for pending_attestation in state.current_epoch_attestations:
diff --git a/specs/phase1/fork-choice.md b/specs/phase1/fork-choice.md
index f92640ebb..41787cfd0 100644
--- a/specs/phase1/fork-choice.md
+++ b/specs/phase1/fork-choice.md
@@ -39,7 +39,8 @@ class LatestMessage(object):
 def update_latest_messages(store: Store, attesting_indices: Sequence[ValidatorIndex], attestation: Attestation) -> None:
     target = attestation.data.target
     beacon_block_root = attestation.data.beacon_block_root
-    shard = get_shard(store.block_states[beacon_block_root], attestation)
+    # TODO: separate shard chain vote
+    shard = attestation.data.shard
     for i in attesting_indices:
         if i not in store.latest_messages or target.epoch > store.latest_messages[i].epoch:
             store.latest_messages[i] = LatestMessage(
diff --git a/specs/phase1/shard-transition.md b/specs/phase1/shard-transition.md
index 083064225..50694ce68 100644
--- a/specs/phase1/shard-transition.md
+++ b/specs/phase1/shard-transition.md
@@ -124,8 +124,7 @@ def is_valid_fraud_proof(beacon_state: BeaconState,
     # 2. Check if the shard state transition result is wrong between
     # `transition.shard_states[offset_index - 1]` to `transition.shard_states[offset_index]`.
     if offset_index == 0:
-        shard = get_shard(beacon_state, attestation)
-        shard_states = beacon_parent_block.body.shard_transitions[shard].shard_states
+        shard_states = beacon_parent_block.body.shard_transitions[attestation.data.shard].shard_states
         shard_state = shard_states[len(shard_states) - 1]
     else:
         shard_state = transition.shard_states[offset_index - 1]  # Not doing the actual state updates here.
diff --git a/tests/core/pyspec/eth2spec/test/fork_choice/test_on_attestation.py b/tests/core/pyspec/eth2spec/test/fork_choice/test_on_attestation.py
index 2c50544d8..c1a5b2b33 100644
--- a/tests/core/pyspec/eth2spec/test/fork_choice/test_on_attestation.py
+++ b/tests/core/pyspec/eth2spec/test/fork_choice/test_on_attestation.py
@@ -26,7 +26,7 @@ def run_on_attestation(spec, state, store, attestation, valid=True):
         latest_message = spec.LatestMessage(
             epoch=attestation.data.target.epoch,
             root=attestation.data.beacon_block_root,
-            shard=spec.get_shard(state, attestation),
+            shard=attestation.data.shard,
             shard_root=attestation.data.shard_head_root,
         )
 
diff --git a/tests/core/pyspec/eth2spec/test/fork_choice/test_on_shard_head.py b/tests/core/pyspec/eth2spec/test/fork_choice/test_on_shard_head.py
index 24eeaedbe..c84f073b2 100644
--- a/tests/core/pyspec/eth2spec/test/fork_choice/test_on_shard_head.py
+++ b/tests/core/pyspec/eth2spec/test/fork_choice/test_on_shard_head.py
@@ -82,7 +82,7 @@ def apply_shard_and_beacon(spec, state, store, shard_store, shard_blocks_buffer)
             shard_transition=shard_transition,
             signed=False,
         )
-        assert spec.get_shard(state, attestation) == shard
+        assert attestation.data.shard == shard
         beacon_block.body.attestations = [attestation]
         beacon_block.body.shard_transitions = shard_transitions
 
diff --git a/tests/core/pyspec/eth2spec/test/helpers/attestations.py b/tests/core/pyspec/eth2spec/test/helpers/attestations.py
index 23eba34da..52f2ca157 100644
--- a/tests/core/pyspec/eth2spec/test/helpers/attestations.py
+++ b/tests/core/pyspec/eth2spec/test/helpers/attestations.py
@@ -46,7 +46,7 @@ def run_attestation_processing(spec, state, attestation, valid=True):
     yield 'post', state
 
 
-def build_attestation_data(spec, state, slot, index, shard_transition=None, on_time=True):
+def build_attestation_data(spec, state, slot, index, shard=None, shard_transition=None, on_time=True):
     assert state.slot >= slot
 
     if slot == state.slot:
@@ -78,13 +78,15 @@ def build_attestation_data(spec, state, slot, index, shard_transition=None, on_t
     )
 
     if spec.fork == PHASE1:
+        if shard is None:
+            shard = spec.compute_shard_from_committee_index(state, attestation_data.index, attestation_data.slot)
+        attestation_data.shard = shard
+
         if shard_transition is not None:
             lastest_shard_data_root_index = len(shard_transition.shard_data_roots) - 1
             attestation_data.shard_head_root = shard_transition.shard_data_roots[lastest_shard_data_root_index]
             attestation_data.shard_transition_root = shard_transition.hash_tree_root()
         else:
-            # No shard transition -> no shard block
-            shard = spec.get_shard(state, spec.Attestation(data=attestation_data))
             if on_time:
                 shard_transition = spec.get_shard_transition(state, shard, shard_blocks=[])
                 lastest_shard_data_root_index = len(shard_transition.shard_data_roots) - 1