diff --git a/sbin/ipfw/ipv6.c b/sbin/ipfw/ipv6.c
index 7f30a1df7bcb..050cb6d42941 100644
--- a/sbin/ipfw/ipv6.c
+++ b/sbin/ipfw/ipv6.c
@@ -143,6 +143,7 @@ fill_icmp6types(ipfw_insn_icmp6 *cmd, char *av, int cblen)
        uint8_t type;
 
        CHECK_LENGTH(cblen, F_INSN_SIZE(ipfw_insn_icmp6));
+       memset(cmd, 0, sizeof(*cmd));
        while (*av) {
 	       if (*av == ',')
 		       av++;