diff --git a/bgpd/bgp_attr.h b/bgpd/bgp_attr.h
index b59fa8e..6fdf1c1 100644
--- a/bgpd/bgp_attr.h
+++ b/bgpd/bgp_attr.h
@@ -205,6 +205,8 @@
 extern void bgp_packet_mpattr_prefix(struct stream *s, afi_t afi, safi_t safi,
 				     struct prefix *p, struct prefix_rd *prd,
 				     u_char *tag);
+extern size_t bgp_packet_mpattr_prefix_size(afi_t afi, safi_t safi,
+                                            struct prefix *p);
 extern void bgp_packet_mpattr_end(struct stream *s, size_t sizep);
 
 extern size_t bgp_packet_mpunreach_start (struct stream *s, afi_t afi,