diff --git a/specs/phase1/shard-fork-choice.md b/specs/phase1/shard-fork-choice.md
index b026aabfc..867730203 100644
--- a/specs/phase1/shard-fork-choice.md
+++ b/specs/phase1/shard-fork-choice.md
@@ -59,7 +59,9 @@ def get_shard_latest_attesting_balance(store: Store, shard_store: ShardStore, ro
     return Gwei(sum(
         state.validators[i].effective_balance for i in active_indices
         if (
-            i in store.latest_messages and get_shard_ancestor(
+            i in store.latest_messages and
+            store.latest_messages[i].shard == shard_store.shard and
+            get_shard_ancestor(
                 store, shard_store, store.latest_messages[i].root, shard_store.blocks[root].slot
             ) == root
         )
@@ -71,12 +73,18 @@ def get_shard_latest_attesting_balance(store: Store, shard_store: ShardStore, ro
 ```python
 def get_shard_head(store: Store, shard_store: ShardStore) -> Root:
     # Execute the LMD-GHOST fork choice
+    shard_blocks = shard_store.blocks
     head_beacon_root = get_head(store)
-    head_shard_root = store.block_states[head_beacon_root].shard_states[shard_store.shard].latest_block_root
+    head_shard_state = store.block_states[head_beacon_root].shard_states[shard_store.shard]
+    head_shard_root = head_shard_state.latest_block_root
     while True:
+        # Find the valid child block roots
         children = [
             root for root in shard_store.blocks.keys()
-            if shard_store.blocks[root].shard_parent_root == head_shard_root
+            if (
+                shard_blocks[root].shard_parent_root == head_shard_root
+                and shard_blocks[root].slot > head_shard_state.slot
+            )
         ]
         if len(children) == 0:
             return head_shard_root
@@ -116,14 +124,15 @@ def on_shard_block(store: Store, shard_store: ShardStore, signed_shard_block: Si
     assert shard_block.beacon_parent_root in store.block_states
     beacon_state = store.block_states[shard_block.beacon_parent_root]
 
-    # 3. Check that block is later than the finalized epoch slot (optimization to reduce calls to get_ancestor)
-    finalized_slot = compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)
-    assert shard_block.slot > finalized_slot
+    # 3. Check that block is later than the finalized shard state slot (optimization to reduce calls to get_ancestor)
+    finalized_beacon_state = store.block_states[store.finalized_checkpoint.root]
+    finalized_shard_state = finalized_beacon_state.shard_states[shard]
+    assert shard_block.slot > finalized_shard_state.slot
 
     # 4. Check block is a descendant of the finalized block at the checkpoint finalized slot
+    finalized_slot = compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)
     assert (
-        shard_block.beacon_parent_root == store.finalized_checkpoint.root
-        or get_ancestor(store, shard_block.beacon_parent_root, finalized_slot) == store.finalized_checkpoint.root
+        get_ancestor(store, shard_block.beacon_parent_root, finalized_slot) == store.finalized_checkpoint.root
     )
 
     # Add new block to the store