diff --git a/zebra/rtadv.c b/zebra/rtadv.c
index 082a1b3..7ded4c8 100644
--- a/zebra/rtadv.c
+++ b/zebra/rtadv.c
@@ -283,7 +283,7 @@
   msg.msg_iov = &iov;
   msg.msg_iovlen = 1;
   msg.msg_control = (void *) adata;
-  msg.msg_controllen = CMSG_LEN(sizeof(struct in6_pktinfo));
+  msg.msg_controllen = CMSG_SPACE(sizeof(struct in6_pktinfo));
   msg.msg_flags = 0;
   iov.iov_base = buf;
   iov.iov_len = len;