diff --git a/src/flask/wrappers.py b/src/flask/wrappers.py
index bf31fc56..7153876b 100644
--- a/src/flask/wrappers.py
+++ b/src/flask/wrappers.py
@@ -123,7 +123,7 @@ class Request(RequestBase):
 
             attach_enctype_error_multidict(self)
 
-    def on_json_loading_failed(self, e: ValueError) -> t.Any:
+    def on_json_loading_failed(self, e: t.Optional[ValueError]) -> t.Any:
         try:
             return super().on_json_loading_failed(e)
         except BadRequest as e: