diff --git a/stdlib/argparse.pyi b/stdlib/argparse.pyi
index 44f39c8c92d1..1bdcace7d897 100644
--- a/stdlib/argparse.pyi
+++ b/stdlib/argparse.pyi
@@ -399,6 +399,10 @@ class _StoreFalseAction(_StoreConstAction):
 # undocumented
 class _AppendAction(Action): ...
 
+# undocumented
+if sys.version_info >= (3, 8):
+    class _ExtendAction(_AppendAction): ...
+
 # undocumented
 class _AppendConstAction(Action):
     if sys.version_info >= (3, 11):