diff --git a/src/flask/scaffold.py b/src/flask/scaffold.py
index 8a87ad32..4814a232 100644
--- a/src/flask/scaffold.py
+++ b/src/flask/scaffold.py
@@ -646,7 +646,9 @@ class Scaffold:
         return f
 
     @setupmethod
-    def errorhandler(self, code_or_exception: t.Union[T, int]) -> T:
+    def errorhandler(
+        self, code_or_exception: t.Union[t.Type[GenericException], int]
+    ) -> T:
         """Register a function to handle errors by code or exception class.
 
         A decorator that is used to register a function given an