diff --git a/specs/core/1_shard-data-chains.md b/specs/core/1_shard-data-chains.md
index f284574f2..317011716 100644
--- a/specs/core/1_shard-data-chains.md
+++ b/specs/core/1_shard-data-chains.md
@@ -432,7 +432,7 @@ def shard_slot_transition(state: ShardState, beacon_state: BeaconState) -> None:
     # Save states in history accumulator
     depth = 0
     h = hash_tree_root(state)
-    while state.slot % 2**depth == 0 and depth <= HISTORY_ACCUMULATOR_VECTOR:
+    while state.slot % 2**depth == 0 and depth < HISTORY_ACCUMULATOR_VECTOR:
         state.history_accumulator[depth] = h
         depth += 1