diff --git a/lib/sockopt.c b/lib/sockopt.c
index 1f9f527..6e1feec 100644
--- a/lib/sockopt.c
+++ b/lib/sockopt.c
@@ -313,6 +313,7 @@
 
 #ifdef HAVE_STRUCT_IP_MREQN_IMR_IFINDEX
   struct ip_mreqn mreqn;
+  memset (&mreqn, 0, sizeof(mreqn));
 
   mreqn.imr_ifindex = ifindex;
   return setsockopt(sock, IPPROTO_IP, IP_MULTICAST_IF, (void *)&mreqn, sizeof(mreqn));