diff -r 0acc5626a578 Lib/test/test_cmd_line.py
--- a/Lib/test/test_cmd_line.py	Tue Oct 23 22:50:11 2012 +0100
+++ b/Lib/test/test_cmd_line.py	Thu Oct 25 01:40:17 2012 +0300
@@ -358,6 +358,12 @@
         self.assertEqual(rc, 0)
         self.assertIn(b'random is 1', out)
 
+    def test_unknown_options(self):
+        rc, out, err = assert_python_failure('-z', __cleanenv=True)
+        self.assertIn(b'Unknown option', err)
+        self.assertEqual(err.splitlines().count(b'Unknown option: -z'), 1)
+        self.assertEqual(b'', out)
+
 def test_main():
     test.support.run_unittest(CmdLineTest)
     test.support.reap_children()
diff -r 0acc5626a578 Python/getopt.c
--- a/Python/getopt.c	Tue Oct 23 22:50:11 2012 +0100
+++ b/Python/getopt.c	Thu Oct 25 01:40:17 2012 +0300
@@ -45,7 +45,7 @@
 
 void _PyOS_ResetGetOpt(void)
 {
-    _PyOS_opterr = 1;
+    _PyOS_opterr = 0;  /* prevent printing the error in 2nd loop in main.c */
     _PyOS_optind = 1;
     _PyOS_optarg = NULL;
     opt_ptr = L"";
@@ -90,7 +90,7 @@
         opt_ptr = &argv[_PyOS_optind++][1];
     }
 
-    if ( (option = *opt_ptr++) == L'\0')
+    if ((option = *opt_ptr++) == L'\0')
         return -1;
 
     if (option == 'J') {
@@ -100,8 +100,7 @@
 
     if ((ptr = wcschr(optstring, option)) == NULL) {
         if (_PyOS_opterr)
-          fprintf(stderr, "Unknown option: -%c\n", (char)option);
-
+            fprintf(stderr, "Unknown option: -%c\n", (char)option);
         return '_';
     }