diff --git a/certbot/tests/cert_manager_test.py b/certbot/tests/cert_manager_test.py
index bffa5298f..e04e25da8 100644
--- a/certbot/tests/cert_manager_test.py
+++ b/certbot/tests/cert_manager_test.py
@@ -383,7 +383,7 @@ class RenameLineageTest(BaseCertManagerTest):
         mock_config.new_certname = "example.org"
         self.assertRaises(errors.ConfigurationError, self._call, mock_config)
 
-        mock_config.new_certname = "one/two"
+        mock_config.new_certname = "one{0}two".format(os.path.sep)
         self.assertRaises(errors.ConfigurationError, self._call, mock_config)