diff --git a/fastapi/routing.py b/fastapi/routing.py
index 5228c5e20..e28314612 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -1589,7 +1589,7 @@ class _IncludedRouter(BaseRoute):
         with self._rebuild_lock:
             if routes_version == self._effective_candidates_version:
                 return self._effective_candidates
-            new_candidates: list["_EffectiveRouteContext | _IncludedRouter"] = []
+            new_candidates: list[_EffectiveRouteContext | _IncludedRouter] = []
             candidates = self.original_router.routes
             for route in candidates:
                 if isinstance(route, _IncludedRouter):
@@ -1614,7 +1614,7 @@ class _IncludedRouter(BaseRoute):
         with self._rebuild_lock:
             if routes_version == self._effective_low_priority_routes_version:
                 return self._effective_low_priority_routes
-            new_low_priority: list["_EffectiveRouteContext"] = []
+            new_low_priority: list[_EffectiveRouteContext] = []
             for route in self.original_router._low_priority_routes:
                 route_context = self._build_effective_context(route)
                 if route_context is not None:
diff --git a/tests/test_thread_safety.py b/tests/test_thread_safety.py
index aef704bcf..e8dd88dd0 100644
--- a/tests/test_thread_safety.py
+++ b/tests/test_thread_safety.py
@@ -1,4 +1,5 @@
 """Test thread safety of _IncludedRouter cache rebuild."""
+
 import sys
 import threading
 
@@ -15,8 +16,10 @@ def test_effective_candidates_thread_safety():
     app = FastAPI()
     router = APIRouter()
     for i in range(N_ROUTES):
+
         def endpoint(i: int = i):
             return {"i": i}
+
         router.add_api_route(f"/r{i}", endpoint, methods=["GET"])
     app.include_router(router)
 
@@ -42,9 +45,7 @@ def test_effective_candidates_thread_safety():
 
     assert not errors, f"Errors during concurrent requests: {errors}"
 
-    included = next(
-        r for r in app.router.routes if isinstance(r, _IncludedRouter)
-    )
+    included = next(r for r in app.router.routes if isinstance(r, _IncludedRouter))
     n_candidates = len(included._effective_candidates)
     assert n_candidates == N_ROUTES, (
         f"Expected {N_ROUTES} cached candidates, got {n_candidates}"
@@ -59,9 +60,13 @@ def test_effective_low_priority_thread_safety():
     app = FastAPI()
     router = APIRouter()
     for i in range(N_ROUTES):
+
         def endpoint(i: int = i):
             return {"i": i}
-        router.add_api_route(f"/r{i}", endpoint, methods=["GET"], include_in_schema=False)
+
+        router.add_api_route(
+            f"/r{i}", endpoint, methods=["GET"], include_in_schema=False
+        )
     app.include_router(router)
 
     sys.setswitchinterval(1e-5)