diff --git a/ospf6d/ospf6_asbr.h b/ospf6d/ospf6_asbr.h
index 6deb93e..cd1c939 100644
--- a/ospf6d/ospf6_asbr.h
+++ b/ospf6d/ospf6_asbr.h
@@ -44,6 +44,7 @@
 };
 
 /* AS-External-LSA */
+#define OSPF6_AS_EXTERNAL_LSA_MIN_SIZE         4U /* w/o IPv6 prefix */
 struct ospf6_as_external_lsa
 {
   u_int32_t bits_metric;