diff --git a/tests/appservice/test_appservice.py b/tests/appservice/test_appservice.py
index 7586ea905..f943dbfa0 100644
--- a/tests/appservice/test_appservice.py
+++ b/tests/appservice/test_appservice.py
@@ -36,6 +36,7 @@ class ApplicationServiceTestCase(unittest.TestCase):
             id="unique_identifier",
             url="some_url",
             token="some_token",
+            hostname="matrix.org", # only used by get_groups_for_user
             namespaces={
                 ApplicationService.NS_USERS: [],
                 ApplicationService.NS_ROOMS: [],