diff -r b6ebc726d5fe Lib/locale.py
--- a/Lib/locale.py	Sat Jul 06 13:25:44 2013 +0200
+++ b/Lib/locale.py	Sat Jul 06 14:10:50 2013 +0200
@@ -430,6 +430,8 @@
         return tuple(code.split('.')[:2])
     elif code == 'C':
         return None, None
+    elif code == 'UTF-8':
+        return None, code
     raise ValueError('unknown locale: %s' % localename)
 
 def _build_localename(localetuple):
diff -r b6ebc726d5fe Lib/test/test_locale.py
--- a/Lib/test/test_locale.py	Sat Jul 06 13:25:44 2013 +0200
+++ b/Lib/test/test_locale.py	Sat Jul 06 14:10:50 2013 +0200
@@ -414,6 +414,13 @@
         with self.assertRaises(TypeError):
             locale.setlocale(locale.LC_ALL, (b'not', b'valid'))
 
+    def test_parse_utf8_locale(self):
+        """ On Mac OS X with default language set to English, the default
+            terminal sets the LC_CTYPE variable to UTF-8. Make sure we can
+            parse this value rather than fail.
+        """
+        self.assertEqual((None, 'UTF-8'), locale._parse_localename('UTF-8'))
+
 
 def test_main():
     tests = [