diff -r 2358a46b621e Lib/test/test_os.py
--- a/Lib/test/test_os.py	Mon Oct 24 21:22:39 2011 +0300
+++ b/Lib/test/test_os.py	Tue Oct 25 11:40:43 2011 -0700
@@ -1074,6 +1074,47 @@
 
 
 @unittest.skipUnless(sys.platform == "win32", "Win32 specific tests")
+class Win32ListdirTests(unittest.TestCase):
+    """Test listdir on Windows."""
+
+    def setUp(self):
+        self.created_paths = []
+        while len(self.created_paths) < 3:
+            dir_name = 'SUB' + str(len(self.created_paths))
+            dir_path = os.path.join(support.TESTFN, dir_name)
+            file_name = 'FILE' + str(len(self.created_paths))
+            file_path = os.path.join(support.TESTFN, file_name)
+            os.makedirs(dir_path)
+            with open(file_path, 'w') as f:
+                f.write("I'm %s and proud of it. Blame test_os.\n" % file_path)
+            self.created_paths.extend([dir_name, file_name])
+        self.created_paths.sort()
+
+    def tearDown(self):
+        shutil.rmtree(support.TESTFN)
+
+    def test_listdir_no_extended_path(self):
+        """Test when the path is not an "extended" path."""
+        # unicode
+        self.assertEqual(self.created_paths,
+                sorted(os.listdir(support.TESTFN)))
+        # bytes
+        self.assertEqual([os.fsencode(path) for path in self.created_paths],
+                         sorted(os.listdir(os.fsencode(support.TESTFN))))
+
+    def test_listdir_extended_path(self):
+        """Test when the path starts with '\\\\?\\'."""
+        # See: http://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx#maxpath
+        # unicode
+        path = '\\\\?\\' + os.path.abspath(support.TESTFN)
+        self.assertEqual(self.created_paths, sorted(os.listdir(path)))
+        # bytes
+        path = b'\\\\?\\' + os.fsencode(os.path.abspath(support.TESTFN))
+        self.assertEqual([os.fsencode(path) for path in self.created_paths],
+                         sorted(os.listdir(path)))
+
+
+@unittest.skipUnless(sys.platform == "win32", "Win32 specific tests")
 @support.skip_unless_symlink
 class Win32SymlinkTests(unittest.TestCase):
     filelink = 'filelinktest'
@@ -1621,6 +1662,7 @@
         Pep383Tests,
         Win32KillTests,
         Win32SymlinkTests,
+        Win32ListdirTests,
         FSEncodingTests,
         PidTests,
         LoginTests,
diff -r 2358a46b621e Modules/posixmodule.c
--- a/Modules/posixmodule.c	Mon Oct 24 21:22:39 2011 +0300
+++ b/Modules/posixmodule.c	Tue Oct 25 11:40:43 2011 -0700
@@ -2542,8 +2542,8 @@
         wcscpy(wnamebuf, po_wchars);
         if (len > 0) {
             wchar_t wch = wnamebuf[len-1];
-            if (wch != L'/' && wch != L'\\' && wch != L':')
-                wnamebuf[len++] = L'\\';
+            if (wch != SEP && wch != ALTSEP && wch != L':')
+                wnamebuf[len++] = SEP;
             wcscpy(wnamebuf + len, L"*.*");
         }
         if ((d = PyList_New(0)) == NULL) {
@@ -2622,8 +2622,8 @@
     Py_DECREF(opath);
     if (len > 0) {
         char ch = namebuf[len-1];
-        if (ch != SEP && ch != ALTSEP && ch != ':')
-            namebuf[len++] = '/';
+        if (ch != '\\' && ch != '/' && ch != ':')
+            namebuf[len++] = '\\';
         strcpy(namebuf + len, "*.*");
     }