Index: Lib/argparse.py
===================================================================
--- Lib/argparse.py	(revision 86553)
+++ Lib/argparse.py	(working copy)
@@ -382,6 +382,9 @@
         # find group indices and identify actions in groups
         group_actions = set()
         inserts = {}
+        variable_option_usage = any(
+            a.nargs in (OPTIONAL, ONE_OR_MORE, ZERO_OR_MORE)
+            for a in actions if a.option_strings)
         for group in groups:
             try:
                 start = actions.index(group._group_actions[0])
@@ -422,6 +425,11 @@
 
             # produce all arg strings
             elif not action.option_strings:
+                # add -- before the first argument if needed to be unambiguous
+                if variable_option_usage:
+                    parts.append("--")
+                    variable_option_usage = False
+
                 part = self._format_args(action, action.dest)
 
                 # if it's in a group, strip the outer []
Index: Lib/test/test_argparse.py
===================================================================
--- Lib/test/test_argparse.py	(revision 86553)
+++ Lib/test/test_argparse.py	(working copy)
@@ -1238,9 +1238,19 @@
         ('a', NS(x=None, y=['a'])),
         ('a -x', NS(x=[], y=['a'])),
         ('a -x b', NS(x=['b'], y=['a'])),
+        ('-x a b', NS(x=['a','b'], y=[]))
     ]
 
+class TestNargsOneOrMore(ParserTestCase):
+    """Tests specifying an args for an Optional that accepts one or more"""
 
+    argument_signatures = [Sig('-x', nargs='+'), Sig('y')]
+    failures = ['-x a b']
+    successes = [
+        ('-x a -- b', NS(x=['a'], y='b')),
+        ('b -x a', NS(x=['a'], y='b'))
+    ]
+
 class TestNargsRemainder(ParserTestCase):
     """Tests specifying a positional with nargs=REMAINDER"""
 
@@ -2856,7 +2866,7 @@
             Sig('-z', nargs='+', help='Z HELP')]),
     ]
     usage = '''\
-        usage: PROG [-h] [-v] [-x] [--y Y] [-z Z [Z ...]] foo bar baz
+        usage: PROG [-h] [-v] [-x] [--y Y] [-z Z [Z ...]] -- foo bar baz
         '''
     help = usage + '''\
 
@@ -3847,6 +3857,24 @@
         '''
     version = ''
 
+class TestHelpVariableOptionalsNoArgs(HelpTestCase):
+    """Test lacking of -- seperator if no positional arguments can be supplied
+    """
+
+    parser_signature = Sig(prog='PROG')
+    argument_signatures = [Sig('-x', nargs='?')]
+    argument_group_signatures = []
+    usage = '''\
+        usage: PROG [-h] [-x [X]]
+        '''
+    help = usage + '''\
+
+        optional arguments:
+          -h, --help  show this help message and exit
+          -x [X]
+        '''
+    version= ''
+
 # =====================================
 # Optional/Positional constructor tests
 # =====================================