diff --git a/python/sglang/lang/chat_template.py b/python/sglang/lang/chat_template.py
index b8f9a533d..ca5a7a261 100644
--- a/python/sglang/lang/chat_template.py
+++ b/python/sglang/lang/chat_template.py
@@ -144,7 +144,7 @@ register_chat_template(
             "assistant": ("<|im_start|>assistant\n", "<|im_end|>\n"),
         },
         style=ChatTemplateStyle.PLAIN,
-        stop_str=("<|im_end|>"),
+        stop_str=("<|im_end|>",),
         image_token="<|vision_start|><|image_pad|><|vision_end|>",
     )
 )