diff --git a/fastapi/routing.py b/fastapi/routing.py
index 41c3c8aea5..346d96f6ab 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -1795,7 +1795,10 @@ class APIRouter(routing.Router):
                     ),
                 )
                 new_route = self.routes[-1]
-                if isinstance(new_route, APIRoute) and route.stream_item_type is not None:
+                if (
+                    isinstance(new_route, APIRoute)
+                    and route.stream_item_type is not None
+                ):
                     new_route.stream_item_type = route.stream_item_type
                     new_route.stream_item_field = create_model_field(
                         name=f"StreamItem_{new_route.unique_id}",
diff --git a/tests/test_sse.py b/tests/test_sse.py
index 0772376afc..444b745c29 100644
--- a/tests/test_sse.py
+++ b/tests/test_sse.py
@@ -261,9 +261,9 @@ def test_sse_on_router_included_in_app(client: TestClient):
     assert route.stream_item_field is not None
 
     openapi = app.openapi()
-    item_schema = openapi["paths"]["/api/events"]["get"]["responses"]["200"][
-        "content"
-    ]["text/event-stream"]["itemSchema"]
+    item_schema = openapi["paths"]["/api/events"]["get"]["responses"]["200"]["content"][
+        "text/event-stream"
+    ]["itemSchema"]
     assert "contentSchema" in item_schema["properties"]["data"]
     assert "Item" in openapi["components"]["schemas"]