diff --git a/sys/netinet/in.h b/sys/netinet/in.h
index 4f4765819d2f..9eb3b177c169 100644
--- a/sys/netinet/in.h
+++ b/sys/netinet/in.h
@@ -236,6 +236,7 @@ __END_DECLS
 #define	IPPROTO_GMTP		100		/* GMTP*/
 #define	IPPROTO_IPCOMP		108		/* payload compression (IPComp) */
 #define	IPPROTO_SCTP		132		/* SCTP */
+#define	IPPROTO_MH		135		/* IPv6 Mobility Header */
 /* 101-254: Partly Unassigned */
 #define	IPPROTO_PIM		103		/* Protocol Independent Mcast */
 #define	IPPROTO_CARP		112		/* CARP */