diff --git a/synapse/handlers/e2e_room_keys.py b/synapse/handlers/e2e_room_keys.py
index cad38d2bdd..9abaf13b8f 100644
--- a/synapse/handlers/e2e_room_keys.py
+++ b/synapse/handlers/e2e_room_keys.py
@@ -210,8 +210,7 @@ class E2eRoomKeysHandler(object):
                     if not isinstance(room_key["is_verified"], bool):
                         msg = (
                             "is_verified must be a boolean in keys for session %s in"
-                            "room %s"
-                            % (session_id, room_id)
+                            "room %s" % (session_id, room_id)
                         )
                         raise SynapseError(400, msg, Codes.INVALID_PARAM)