diff --git a/src/osmo_ms_driver/location_update_test.py b/src/osmo_ms_driver/location_update_test.py
index e83d91b..010c278 100644
--- a/src/osmo_ms_driver/location_update_test.py
+++ b/src/osmo_ms_driver/location_update_test.py
@@ -83,6 +83,7 @@
         self._event_server = event_server
         self._event_server.register(self.handle_msg)
         self._unstarted = copy(self._mobiles)
+        self._started = []
 
     def mobiles(self):
         return self._mobiles