diff --git a/course/tests/externallib_test.php b/course/tests/externallib_test.php
index 984b9ed3588..605c5d8ec4b 100644
--- a/course/tests/externallib_test.php
+++ b/course/tests/externallib_test.php
@@ -580,5 +580,6 @@ class core_course_external_testcase extends externallib_advanced_testcase {
 
         // Check that the course has been duplicated.
         $this->assertEquals($newcourse['shortname'], $duplicate['shortname']);
+        gc_collect_cycles();
     }
 }