diff --git a/specs/beacon-chain.md b/specs/beacon-chain.md
index 04664e114..16be55464 100644
--- a/specs/beacon-chain.md
+++ b/specs/beacon-chain.md
@@ -119,16 +119,21 @@ An `AttestationRecord` has the following fields:
 }
 ```
 
-Here's the data signed (`AttestationSignedData`):
+An `AttestationSignedData` has the following fields:
 
 ```python
-fields = {
-    # Version of the chain
+{
+    # Chain version
     'version': 'int64',
+    # Slot number
     'slot': 'int64',
+    # Shard number
+    'shard': 'int16',
+    # 31 parent hashes
     'parent_hashes': ['hash32'],
-    'shard_id': 'int16',
+    # Shard block hash
     'shard_block_hash': 'hash32',
+    # Slot of last justified block
     'justified_slot': 'int64'
 }
 ```
@@ -491,7 +496,7 @@ For each one of these attestations:
 * Verify that `len(attester_bitfield) == ceil_div8(len(attestation_indices))`, where `ceil_div8 = (x + 7) // 8`. Verify that bits `len(attestation_indices)....` and higher, if present (i.e. `len(attestation_indices)` is not a multiple of 8), are all zero
 * Derive a group public key by adding the public keys of all of the attesters in `attestation_indices` for whom the corresponding bit in `attester_bitfield` (the ith bit is `(attester_bitfield[i // 8] >> (7 - (i %8))) % 2`) equals 1
 * Let `version = pre_fork_version if slot < fork_slot_number else post_fork_version`.
-* Verify that `aggregate_sig` verifies using the group pubkey generated and the serialized form of `AttestationSignedData(version, slot, parent_hashes, shard_id, shard_block_hash, justified_slot)` as the message.
+* Verify that `aggregate_sig` verifies using the group pubkey generated and the serialized form of `AttestationSignedData(version, slot, parent_hashes, shard, shard_block_hash, justified_slot)` as the message.
 
 Extend the list of `AttestationRecord` objects in the `active_state` with those included in the block, ordering the new additions in the same order as they came in the block. Similarly extend the list of `SpecialRecord` objects in the `active_state` with those included in the block.