diff --git a/lib/sockopt.c b/lib/sockopt.c
index be22827..97592bb 100644
--- lib/sockopt.c
+++ lib/sockopt.c
@@ -339,6 +339,45 @@ setsockopt_ipv4_multicast_if(int sock,
   m.s_addr = htonl(ifindex);

   return setsockopt (sock, IPPROTO_IP, IP_MULTICAST_IF, (void *)&m, sizeof(m));
+#elif defined(SUNOS_5)
+  struct lifnum    lifn;
+  struct lifconf   lifc;
+  struct lifreq   *lifr;
+
+  lifn.lifn_family = AF_INET;
+  lifn.lifn_flags = 0;
+  if (ioctl(sock,SIOCGLIFNUM,&lifn) == -1) {
+    return -1;
+  }
+  lifc.lifc_family = AF_INET;
+  lifc.lifc_len = lifn.lifn_count * sizeof(struct lifreq);
+  lifc.lifc_buf = malloc(lifc.lifc_len);
+
+  if (lifc.lifc_buf == NULL) {
+    return -1; // failed to allocate memory: return different res?
+  }
+  /* the following ioctl should fail if the system has grown additonal
+     interfaces since we called ioctl(SIOCGLIFNUM) */
+  int res;
+  if ((res = ioctl(sock,SIOCGLIFCONF,&lifc)) >= 0) {
+    lifr = lifc.lifc_req;
+    res = -1;
+    int n;
+    struct in_addr a;
+    /* using lifc.lifc_len, just in  case some interfaces disappeared
+       since ioctl(SIOCGLIFNUM) */
+    for (n = lifc.lifc_len / sizeof(struct lifreq); n > 0; n--) {
+      a=((struct sockaddr_in *)&lifr->lifr_addr)->sin_addr;
+      ioctl(sock,SIOCGLIFINDEX,lifr);
+      if (lifr->lifr_index == ifindex) {
+       res = ioctl(sock,IPPROTO_IP,IP_MULTICAST_IF,&a,sizeof(a));
+       break;
+      }
+      lifr++;
+    }
+  }
+  free(lifc.lifc_buf);
+  return res;
 #else
   #error "Unsupported multicast API"
 #endif