diff --git a/sys/sys/ck.h b/sys/sys/ck.h
index 3bfce70c8d2c..b04fe67b476d 100644
--- a/sys/sys/ck.h
+++ b/sys/sys/ck.h
@@ -1,13 +1,18 @@
 /*
  * $FreeBSD$
  */
+#ifndef _SYS_CK_H_
+#define _SYS_CK_H_
+
 #ifdef _KERNEL
 #include <ck_queue.h>
 #include <ck_epoch.h>
 #else
 #include <sys/queue.h>
 #define CK_STAILQ_HEAD STAILQ_HEAD
 #define CK_STAILQ_ENTRY STAILQ_ENTRY
 #define CK_LIST_HEAD LIST_HEAD
 #define CK_LIST_ENTRY LIST_ENTRY
 #endif
+
+#endif /* !_SYS_CK_H_ */