diff --git a/sys/netinet/libalias/alias_db.h b/sys/netinet/libalias/alias_db.h
index 971ca305c1a..26f055b2987 100644
--- a/sys/netinet/libalias/alias_db.h
+++ b/sys/netinet/libalias/alias_db.h
@@ -273,6 +273,7 @@ struct alias_link {
#define LINK_FRAGMENT_PTR (IPPROTO_MAX + 2)
#define LINK_ADDR (IPPROTO_MAX + 3)
#define LINK_PPTP (IPPROTO_MAX + 4)
+#define LINK_SYNC_MASK 0x80000000
int flags; /* indicates special characteristics */
int pflags; /* protocol-specific flags */
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