diff --git a/python/sglang/bench_serving.py b/python/sglang/bench_serving.py
index cc2406846..4d733e959 100644
--- a/python/sglang/bench_serving.py
+++ b/python/sglang/bench_serving.py
@@ -195,7 +195,8 @@ async def async_request_openai_completions(
                                     output.ttft = ttft
 
                                 # Decoding phase
-                                output.itl.append(timestamp - most_recent_timestamp)
+                                else:
+                                    output.itl.append(timestamp - most_recent_timestamp)
 
                                 most_recent_timestamp = timestamp
                                 generated_text += data["choices"][0]["text"]