diff -r 36af3566b67a Lib/argparse.py
--- a/Lib/argparse.py	Thu Nov 03 15:38:58 2016 +0200
+++ b/Lib/argparse.py	Fri Nov 04 15:16:07 2016 -0400
@@ -1978,7 +1978,8 @@
         required_actions = []
         for action in self._actions:
             if action not in seen_actions:
-                if action.required:
+                if (action.required and
+                    action.nargs not in [OPTIONAL, ZERO_OR_MORE]):
                     required_actions.append(_get_action_name(action))
                 else:
                     # Convert action default now instead of doing it before