diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py
index 11178753ad2..2fb7d1b6d6b 100644
--- a/Lib/test/test_os.py
+++ b/Lib/test/test_os.py
@@ -892,7 +892,7 @@ def test_walk_bottom_up(self):
         # Walk bottom-up.
         all = list(self.walk(self.walk_path, topdown=False))
 
-        self.assertEqual(len(all), 4)
+        self.assertEqual(len(all), 4, all)
         # We can't know which order SUB1 and SUB2 will appear in.
         # Not flipped:  SUB11, SUB1, SUB2, TESTFN
         #     flipped:  SUB2, SUB11, SUB1, TESTFN