diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index d7b9cd8..73ef6f5 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -758,6 +758,7 @@
         old = sys.getfilesystemencoding()
         sys.setfilesystemencoding("iso-8859-1")
         self.assertEqual(sys.getfilesystemencoding(), "iso-8859-1")
+        self.assertRaises(LookupError, sys.setfilesystemencoding, "xxx")
         sys.setfilesystemencoding(old)
 
 def test_main():