diff --git a/ChangeLog b/ChangeLog
index 8b9459f1a0..d4420f0afb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Mon Feb  2 14:22:56 2009  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* ext/socket/constants.c (cmsg_type_arg): INET6 check.
+
 Mon Feb  2 14:18:20 2009  Tanaka Akira  <akr@fsij.org>
 
 	* ext/socket/option.c: use INET6 instead of IPV6.
diff --git a/ext/socket/constants.c b/ext/socket/constants.c
index ea1e0f18fe..bb817e70d9 100644
--- a/ext/socket/constants.c
+++ b/ext/socket/constants.c
@@ -100,8 +100,10 @@ cmsg_type_arg(int level, VALUE optname)
         return constant_arg(optname, scm_optname_to_int, "unknown UNIX control message");
       case IPPROTO_IP:
         return constant_arg(optname, ip_optname_to_int, "unknown IP control message");
+#ifdef INET6
       case IPPROTO_IPV6:
         return constant_arg(optname, ipv6_optname_to_int, "unknown IPv6 control message");
+#endif
       case IPPROTO_TCP:
         return constant_arg(optname, tcp_optname_to_int, "unknown TCP control message");
       case IPPROTO_UDP: