--- a/include/linux/netfilter.h
+++ b/include/linux/netfilter.h
@@ -1,6 +1,7 @@
 #ifndef __LINUX_NETFILTER_H
 #define __LINUX_NETFILTER_H
 
+#include <linux/types.h>
 
 /* Responses from hook functions. */
 #define NF_DROP 0