diff --git a/Lib/test/test_errno.py b/Lib/test/test_errno.py
index 3f44965..e42c86d 100755
--- a/Lib/test/test_errno.py
+++ b/Lib/test/test_errno.py
@@ -42,7 +42,8 @@
         errors_set = set(errors)
         for attribute in errno.__dict__.iterkeys():
             if attribute.isupper():
-                self.assert_(attribute in errors_set)
+                self.assert_(attribute in errors_set,
+                                "%s is an unexpected error value" % attribute)
 
     def test_using_errorcode(self):
         # Every key value in errno.errorcode should be on the module.