diff --git a/python/sglang/srt/entrypoints/openai/protocol.py b/python/sglang/srt/entrypoints/openai/protocol.py
index 23830d86c..0ff49f135 100644
--- a/python/sglang/srt/entrypoints/openai/protocol.py
+++ b/python/sglang/srt/entrypoints/openai/protocol.py
@@ -339,7 +339,7 @@ class FunctionResponse(BaseModel):
     """Function response."""
 
     name: Optional[str] = None
-    arguments: Optional[str] = None
+    arguments: Optional[str | Dict[str, Any]] = None
 
 
 class ToolCall(BaseModel):