diff --git a/Lib/argparse.py b/Lib/argparse.py
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -555,8 +555,8 @@
         if action.metavar is not None:
             result = action.metavar
         elif action.choices is not None:
-            choice_strs = [str(choice) for choice in action.choices]
-            result = '{%s}' % ','.join(choice_strs)
+            result = action._choices_str(',', str, format='{%s}',
+                                         default=default_metavar)
         else:
             result = default_metavar
 
@@ -594,8 +594,11 @@
         for name in list(params):
             if hasattr(params[name], '__name__'):
                 params[name] = params[name].__name__
-        if params.get('choices') is not None:
-            choices_str = ', '.join([str(c) for c in params['choices']])
+        if action.choices is not None:
+            metavar = action.metavar
+            if metavar is None:
+                metavar = self._get_default_metavar(action)
+            choices_str = action._choices_str(', ', str, default=metavar)
             params['choices'] = choices_str
         return self._get_help_string(action) % params
 
@@ -621,6 +624,11 @@
     def _get_help_string(self, action):
         return action.help
 
+    def _get_default_metavar(self, action):
+        if action.option_strings:
+            return self._get_default_metavar_for_optional(action)
+        return self._get_default_metavar_for_positional(action)
+
     def _get_default_metavar_for_optional(self, action):
         return action.dest.upper()
 
@@ -816,6 +824,14 @@
         ]
         return [(name, getattr(self, name)) for name in names]
 
+    def _choices_str(self, sep, to_str, format='%s', default=''):
+        try:
+            choices = iter(self.choices)
+        except TypeError:
+            return default
+        choices_str = sep.join([to_str(choice) for choice in choices])
+        return format % choices_str
+
     def __call__(self, parser, namespace, values, option_string=None):
         raise NotImplementedError(_('.__call__() not defined'))
 
@@ -2294,9 +2310,9 @@
     def _check_value(self, action, value):
         # converted value must be one of the choices (if specified)
         if action.choices is not None and value not in action.choices:
-            args = {'value': value,
-                    'choices': ', '.join(map(repr, action.choices))}
-            msg = _('invalid choice: %(value)r (choose from %(choices)s)')
+            end = action._choices_str(', ', repr, format=' (choose from %s)')
+            args = {'value': value, 'ending': end}
+            msg = _('invalid choice: %(value)r%(ending)s')
             raise ArgumentError(action, msg % args)
 
     # =======================