diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index 8a9da5b..eb50bbb 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -579,7 +579,7 @@
             expected = 'mbcs'
         else:
             expected = None
-        self.check_fsencoding(fs_encoding)
+        self.check_fsencoding(fs_encoding, expected)
 
     @unittest.skipIf(sys.platform in ('win32', 'darwin'),
                      'PYTHONFSENCODING is ignored on Windows and Mac OS X')