--- a/net/ipv4/fou.c
+++ b/net/ipv4/fou.c
@@ -1061,6 +1061,9 @@ static int gue_err(struct sk_buff *skb, u32 info)
        if (validate_gue_flags(guehdr, optlen))
                return -EINVAL;
 
+       if (guehdr->proto_ctype == IPPROTO_UDP)
+               return -EOPNOTSUPP;
+
        skb_set_transport_header(skb, -(int)sizeof(struct icmphdr));
        ret = gue_err_proto_handler(guehdr->proto_ctype, skb, info);