diff --git a/lib/acl_threadsupport/test/acl_threadsupport_test.cpp b/lib/acl_threadsupport/test/acl_threadsupport_test.cpp
index 04fc75b7..01f5d6a8 100644
--- a/lib/acl_threadsupport/test/acl_threadsupport_test.cpp
+++ b/lib/acl_threadsupport/test/acl_threadsupport_test.cpp
@@ -103,7 +103,10 @@ void *test_thread(void *) {
         break;
       acl_thread_yield();
     }
-    if (threadtest_state == END_STATE) {
+    acl_mutex_lock(&mymutex);
+    const bool is_end_state = (threadtest_state == END_STATE);
+    acl_mutex_unlock(&mymutex);
+    if (is_end_state) {
       return 0;
     }
     // CLIENT_STATE