diff --git a/core/mutex.c b/core/mutex.c
index a2ab285a891e8df3d0217e31f4b41d37d1d1af8d..bbc80bc51b959222bf77c0f79144376339e785fa 100644
--- a/core/mutex.c
+++ b/core/mutex.c
@@ -85,7 +85,7 @@ static void mutex_wait(struct mutex_t *mutex)
 void mutex_unlock(struct mutex_t *mutex)
 {
     unsigned irqstate = disableIRQ();
-    DEBUG("mutex_unlock(): val: %u pid: %" PRIkernel_pid "\n", mutex->val, sched_active_pid);
+    DEBUG("mutex_unlock(): val: %u pid: %" PRIkernel_pid "\n", ATOMIC_VALUE(mutex->val), sched_active_pid);
 
     if (ATOMIC_VALUE(mutex->val) == 0) {
         /* the mutex was not locked */