diff --git a/include/netlink/route/cls/fw.h b/include/netlink/route/cls/fw.h
index d1f1b75..2e1bade 100644
--- a/include/netlink/route/cls/fw.h
+++ b/include/netlink/route/cls/fw.h
@@ -22,6 +22,7 @@ extern "C" {
 #endif
 
 extern int	rtnl_fw_set_classid(struct rtnl_cls *, uint32_t);
+extern int	rtnl_fw_set_mask(struct rtnl_cls *, uint32_t);
 
 #ifdef __cplusplus
 }