diff --git a/Lib/argparse.py b/Lib/argparse.py
index 30bae57..6b00239 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1087,7 +1087,14 @@ class _SubParsersAction(Action):
         # parse all the remaining options into the namespace
         # store any unrecognized options on the object, so that the top
         # level parser can decide what to do with them
-        namespace, arg_strings = parser.parse_known_args(arg_strings, namespace)
+
+        # In case this subparser defines new defaults, we parse them
+        # in a new namespace object and then update the original
+        # namespace for the relevant parts.
+        subnamespace, arg_strings = parser.parse_known_args(arg_strings, None)
+        for key, value in vars(subnamespace).items:
+            setattr(namespace, key, value)
+
         if arg_strings:
             vars(namespace).setdefault(_UNRECOGNIZED_ARGS_ATTR, [])
             getattr(namespace, _UNRECOGNIZED_ARGS_ATTR).extend(arg_strings)
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index 30fdf4a..0bc662f 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -2723,6 +2723,13 @@ class TestSetDefaults(TestCase):
         parser = ErrorRaisingArgumentParser(parents=[parent])
         self.assertEqual(NS(x='foo'), parser.parse_args([]))
 
+    def test_set_defaults_on_parent_and_subparser(self):
+        parser = argparse.ArgumentParser()
+        xparser = parser.add_subparsers().add_parser('X')
+        parser.set_defaults(foo=1)
+        xparser.set_defaults(foo=2)
+        self.assertEqual(NS(foo=2), parser.parse_args(['X']))
+
     def test_set_defaults_same_as_add_argument(self):
         parser = ErrorRaisingArgumentParser()
         parser.set_defaults(w='W', x='X', y='Y', z='Z')