diff --git a/kernel/rtmutex-tester.c b/kernel/rtmutex-tester.c
index 6dcea9d..015fc63 100644
--- a/kernel/rtmutex-tester.c
+++ b/kernel/rtmutex-tester.c
@@ -13,6 +13,7 @@
 #include <linux/spinlock.h>
 #include <linux/sysdev.h>
 #include <linux/timer.h>
+#include <linux/freezer.h>
 
 #include "rtmutex.h"