diff -r 10d0a692b1b6 Lib/argparse.py
--- a/Lib/argparse.py	Wed Aug 20 07:55:53 2014 +0530
+++ b/Lib/argparse.py	Wed Aug 20 15:10:11 2014 +0300
@@ -1572,6 +1572,21 @@
         self._group_actions.remove(action)
 
 
+def _prog_name(prog):
+    if prog is not None:
+        return prog
+
+    prog = _os.path.basename(_sys.argv[0])
+
+    if prog != '__main__.py':
+        return prog
+
+    # If prog == '__main__.py' then "python -m module" was called
+    mod = _sys.modules['__main__'].__package__
+    py = _os.path.basename(_sys.executable)
+    return '%s -m %s' % (py, mod)
+
+
 class ArgumentParser(_AttributeHolder, _ActionsContainer):
     """Object for parsing command line strings into Python objects.
 
@@ -1609,11 +1624,7 @@
                   argument_default=argument_default,
                   conflict_handler=conflict_handler)
 
-        # default setting for prog
-        if prog is None:
-            prog = _os.path.basename(_sys.argv[0])
-
-        self.prog = prog
+        self.prog = _prog_name(prog)
         self.usage = usage
         self.epilog = epilog
         self.formatter_class = formatter_class
diff -r 10d0a692b1b6 Lib/test/test_argparse.py
--- a/Lib/test/test_argparse.py	Wed Aug 20 07:55:53 2014 +0530
+++ b/Lib/test/test_argparse.py	Wed Aug 20 15:10:11 2014 +0300
@@ -2223,7 +2223,7 @@
         parents = [self.abcd_parent, self.wxyz_parent]
         parser = ErrorRaisingArgumentParser(parents=parents)
         parser_help = parser.format_help()
-        progname = self.main_program
+        progname = 'python -m test'
         self.assertEqual(parser_help, textwrap.dedent('''\
             usage: {}{}[-h] [-b B] [--d D] [--w W] [-y Y] a z
 
@@ -2257,7 +2257,7 @@
             ['-y', 'Y', '-z', 'Z'])
 
         parser_help = parser.format_help()
-        progname = self.main_program
+        progname = 'python -m test'
         self.assertEqual(parser_help, textwrap.dedent('''\
             usage: {}{}[-h] [-w W] [-x X] [-y Y | -z Z]