diff --git a/fastapi/routing.py b/fastapi/routing.py
index ab0ea0b515..2f0dcc5268 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -100,8 +100,11 @@ def request_response(
     and returns an ASGI application.
     """
     f: Callable[[Request], Awaitable[Response]] = (
-        func if is_async_callable(func) else functools.partial(run_in_threadpool, func)  # type:ignore  # ty: ignore[unused-ignore-comment]
-    )  # ty: ignore
+    f: Callable[[Request], Awaitable[Response]] = (
+        func  # type: ignore[assignment]  # ty: ignore[unused-ignore-comment]
+        if is_async_callable(func)
+        else functools.partial(run_in_threadpool, func)  # type: ignore[call-arg]  # ty: ignore[unused-ignore-comment]
+    )  # ty: ignore[invalid-assignment]
 
     async def app(scope: Scope, receive: Receive, send: Send) -> None:
         request = Request(scope, receive, send)