diff --git a/backend/open_webui/utils/middleware.py b/backend/open_webui/utils/middleware.py
index b9921e382d..e713fad15e 100644
--- a/backend/open_webui/utils/middleware.py
+++ b/backend/open_webui/utils/middleware.py
@@ -5262,9 +5262,10 @@ async def streaming_chat_response_handler(response, ctx):
                             reasoning_item = output[-1]
                             if reasoning_item.get('ended_at') is None:
                                 reasoning_item['ended_at'] = time.time()
-                                reasoning_item['duration'] = int(
-                                    reasoning_item['ended_at'] - reasoning_item['started_at']
-                                )
+                                if reasoning_item.get('started_at') is not None:
+                                    reasoning_item['duration'] = int(
+                                        reasoning_item['ended_at'] - reasoning_item['started_at']
+                                    )
                                 reasoning_item['status'] = 'completed'
 
                     if response_tool_calls: