diff --git a/serve/mlc_serve/engine/sync_engine.py b/serve/mlc_serve/engine/sync_engine.py
index 5250c3870e..075bced22b 100644
--- a/serve/mlc_serve/engine/sync_engine.py
+++ b/serve/mlc_serve/engine/sync_engine.py
@@ -172,7 +172,8 @@ def step(self) -> InferenceStepResult:
             state.token_ids.extend(new_token_ids)
 
         for res in results:
-            state = self.current_batch[res.sequence_id.request_id]
+            request_id = res.sequence_id.request_id
+            state = self.current_batch[request_id]
             delta = self._decode_last_output(state)
             state.output_text += delta