diff --git a/calendar/tests/event_vault_test.php b/calendar/tests/event_vault_test.php
index 1d57d1db9d2..0d522497629 100644
--- a/calendar/tests/event_vault_test.php
+++ b/calendar/tests/event_vault_test.php
@@ -208,7 +208,9 @@ class core_calendar_event_vault_testcase extends advanced_testcase {
         $user = $this->getDataGenerator()->create_user();
         // The factory will skip events with even ids.
         $factory = new action_event_test_factory(function($actionevent) {
-            return ($actionevent->get_id() % 2) ? false : true;
+            static $count = 0;
+            $count++;
+            return ($count % 2) ? true : false;
         });
         $strategy = new raw_event_retrieval_strategy();
         $vault = new event_vault($factory, $strategy);