diff --git a/falcon/asgi/app.py b/falcon/asgi/app.py
index dca7afd96..d28c8c49a 100644
--- a/falcon/asgi/app.py
+++ b/falcon/asgi/app.py
@@ -566,9 +566,7 @@ async def __call__(  # type: ignore[override] # noqa: C901
                             )
 
                             if serialize_sync:
-                                resp._media_rendered = serialize_sync(
-                                    resp._media, resp.content_type
-                                )
+                                resp._media_rendered = serialize_sync(resp._media)
                             else:
                                 resp._media_rendered = await handler.serialize_async(
                                     resp._media, resp.content_type