diff --git a/lib/sockopt.h b/lib/sockopt.h
index 69309e0..aced6d4 100644
--- a/lib/sockopt.h
+++ b/lib/sockopt.h
@@ -35,6 +35,7 @@
 extern int setsockopt_ipv6_unicast_hops (int, int);
 extern int setsockopt_ipv6_hoplimit (int, int);
 extern int setsockopt_ipv6_multicast_loop (int, int);
+extern int setsockopt_ipv6_tclass (int, int);
 #endif /* HAVE_IPV6 */
 
 /*