diff --git a/tests/rest/client/v1/utils.py b/tests/rest/client/v1/utils.py
index 22d734e763..e1fdd7a279 100644
--- a/tests/rest/client/v1/utils.py
+++ b/tests/rest/client/v1/utils.py
@@ -39,7 +39,9 @@ class RestHelper(object):
     resource = attr.ib()
     auth_user_id = attr.ib()
 
-    def create_room_as(self, room_creator=None, is_public=True, tok=None):
+    def create_room_as(
+        self, room_creator: str = None, is_public: bool = True, tok: str = None
+    ) -> str:
         temp_id = self.auth_user_id
         self.auth_user_id = room_creator
         path = "/_matrix/client/r0/createRoom"