diff --git a/stdlib/2and3/argparse.pyi b/stdlib/2and3/argparse.pyi
index 86c23af64..c782b7aea 100644
--- a/stdlib/2and3/argparse.pyi
+++ b/stdlib/2and3/argparse.pyi
@@ -280,6 +280,8 @@ class Action(_AttributeHolder):
     def __call__(self, parser: ArgumentParser, namespace: Namespace,
                  values: Union[Text, Sequence[Any], None],
                  option_string: Optional[Text] = ...) -> None: ...
+    if sys.version_info >= (3, 9):
+        def format_usage(self) -> str: ...
 
 class Namespace(_AttributeHolder):
     def __init__(self, **kwargs: Any) -> None: ...