diff --git a/zaza/openstack/charm_tests/rabbitmq_server/tests.py b/zaza/openstack/charm_tests/rabbitmq_server/tests.py
index 86ec92f..7a84d4a 100644
--- a/zaza/openstack/charm_tests/rabbitmq_server/tests.py
+++ b/zaza/openstack/charm_tests/rabbitmq_server/tests.py
@@ -517,7 +517,7 @@ class RmqRotateServiceUserPasswordTests(test_utils.OpenStackBaseTest):
             'list-service-usernames',
             action_params={}
         )
-        usernames = action.data['results']['usernames'].split(',')
+        usernames = json.loads(action.data['results']['usernames'])
         self.assertIn(CINDER_APP, usernames)
         logging.info("... usernames: %s", ', '.join(usernames))