diff --git a/src/osmo_gsm_tester/ms_driver.py b/src/osmo_gsm_tester/ms_driver.py
index 808989e..a4d81c1 100644
--- a/src/osmo_gsm_tester/ms_driver.py
+++ b/src/osmo_gsm_tester/ms_driver.py
@@ -64,6 +64,7 @@
         self._loop = SimpleLoop()
         self._suite_run.remember_to_stop(self)
         self._test_case = None
+        self.event_server_sk_tmp_dir = None
 
         if len(self.event_server_path().encode()) > 107:
             raise log.Error('Path for event_server socket is longer than max allowed len for unix socket path (107):', self.event_server_path())