diff --git a/chatkit/backend/app/server.py b/chatkit/backend/app/server.py
index 6b8f51f48..2695db56d 100644
--- a/chatkit/backend/app/server.py
+++ b/chatkit/backend/app/server.py
@@ -38,7 +38,7 @@ def __init__(self) -> None:
     async def respond(
         self,
         thread: ThreadMetadata,
-        item: UserMessageItem | None,
+        input_user_message: UserMessageItem | None,
         context: dict[str, Any],
     ) -> AsyncIterator[ThreadStreamEvent]:
         items_page = await self.store.load_thread_items(