diff --git a/src/ts3init_target.c b/src/ts3init_target.c
index 7b8cef3..df16d4c 100644
--- a/src/ts3init_target.c
+++ b/src/ts3init_target.c
@@ -422,6 +422,9 @@ ts3init_morph_to_get_cookie_ipv4_tg(struct sk_buff *skb, const struct xt_action_
 
     udp->len = htons(sizeof(*udp) + sizeof(payload_buf));
     udp->check = 0;
+    udp->check = csum_tcpudp_magic(ip->saddr, ip->daddr,
+	                               ntohs(udp->len), IPPROTO_UDP, 
+								   csum_partial(udp, ntohs(udp->len), 0));
     ip->tot_len = htons(skb->len);
     skb->ip_summed = CHECKSUM_NONE;
 
@@ -457,6 +460,9 @@ ts3init_morph_to_get_cookie_ipv6_tg(struct sk_buff *skb, const struct xt_action_
 
     udp->len = htons(sizeof(*udp) + sizeof(payload_buf));
     udp->check = 0;
+    udp->check = csum_ipv6_magic(&ip->saddr, &ip->daddr,
+	                             ntohs(udp->len), IPPROTO_UDP, 
+								 csum_partial(udp, ntohs(udp->len), 0));
     ip->payload_len = htons(skb->len);
     skb->ip_summed = CHECKSUM_NONE;