diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index d90afda16..0652fecad 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -299,6 +299,7 @@ class ShardBlock(Container):
     shard_parent_root: Root
     beacon_parent_root: Root
     slot: Slot
+    proposer_index: ValidatorIndex
     body: ByteList[MAX_SHARD_BLOCK_SIZE]
 ```
 
@@ -317,6 +318,7 @@ class ShardBlockHeader(Container):
     shard_parent_root: Root
     beacon_parent_root: Root
     slot: Slot
+    proposer_index: ValidatorIndex
     body_root: Root
 ```