diff --git a/tests/unit/customizations/test_preview.py b/tests/unit/customizations/test_preview.py
index 8751b1c203c2..e2a80fe347a2 100644
--- a/tests/unit/customizations/test_preview.py
+++ b/tests/unit/customizations/test_preview.py
@@ -80,4 +80,4 @@ def test_preview_mode_is_in_provider_help(self, renderer):
         contents = renderer.return_value.render.call_args[0][0]
         # The preview services should still be in the help output.
         for service in preview.PREVIEW_SERVICES:
-            self.assertIn(service, contents)
+            self.assertIn(service, contents.decode('utf-8'))