diff --git a/sdk/head/tree.h b/sdk/head/tree.h
index b575509..e94eb56 100644
--- a/sdk/head/tree.h
+++ b/sdk/head/tree.h
@@ -27,7 +27,7 @@
 #ifndef	_SYS_TREE_H_
 #define	_SYS_TREE_H_
 
-#include <stdef.h>
+#include <ptdef.h>
 
 #define __unused ATTR(__unused__)
 #ifndef offsetof