diff --git a/src/flask/sansio/app.py b/src/flask/sansio/app.py
index 01fd5dbf..858403c8 100644
--- a/src/flask/sansio/app.py
+++ b/src/flask/sansio/app.py
@@ -291,7 +291,7 @@ class App(Scaffold):
         instance_path: str | None = None,
         instance_relative_config: bool = False,
         root_path: str | None = None,
-    ):
+    ) -> None:
         super().__init__(
             import_name=import_name,
             static_folder=static_folder,