diff --git a/Lib/test/test_pep277.py b/Lib/test/test_pep277.py
index 862cdbbb864..a7e2f007f39 100644
--- a/Lib/test/test_pep277.py
+++ b/Lib/test/test_pep277.py
@@ -154,7 +154,7 @@ def test_listdir(self):
             sf0 = set(normalize('NFD', f) for f in self.files)
             f2 = [normalize('NFD', f) for f in f2]
         sf2 = set(os.path.join(support.TESTFN, f) for f in f2)
-        self.assertEqual(sf0, sf2)
+        self.assertEqual(sf0, sf2, "%a != %a" % (sf0, sf2))
         self.assertEqual(len(f1), len(f2))
 
     def test_rename(self):