diff --git a/lib/sockopt.h b/lib/sockopt.h
index cb14efc..a9b8aca 100644
--- a/lib/sockopt.h
+++ b/lib/sockopt.h
@@ -83,16 +83,15 @@
   (((af) == AF_INET) : SOPT_SIZE_CMSG_IFINDEX_IPV4() \
                     ? SOPT_SIZE_CMSG_PKTINFO_IPV6())
 
-extern int setsockopt_ipv4_multicast_if(int sock,
-			             unsigned int ifindex);
+extern int setsockopt_ipv4_multicast_if(int sock, ifindex_t ifindex);
 extern int setsockopt_ipv4_multicast(int sock, int optname,
                                      unsigned int mcast_addr,
-			             unsigned int ifindex);
+			             ifindex_t ifindex);
 extern int setsockopt_ipv4_tos(int sock, int tos);
 
 /* Ask for, and get, ifindex, by whatever method is supported. */
-extern int setsockopt_ifindex (int, int, int);
-extern int getsockopt_ifindex (int, struct msghdr *);
+extern int setsockopt_ifindex (int, int, ifindex_t);
+extern ifindex_t getsockopt_ifindex (int, struct msghdr *);
 
 /* swab the fields in iph between the host order and system order expected 
  * for IP_HDRINCL.