pfSense

--- src/igmp.c.orig

+++ src/igmp.c

@@ -295,7 +295,7 @@ static void buildIgmp(uint32_t src, uint32_t dst, int type, int code, uint32_t g

     igmp->igmp_group.s_addr = group;

     igmp->igmp_cksum        = 0;

     igmp->igmp_cksum        = inetChksum((unsigned short *)igmp,

-                                         IP_HEADER_RAOPT_LEN + datalen);

+                                         sizeof(igmp) + datalen);

 }