--- linux-4.9.37/net/ipv4/ip_output.c	2017-07-12 16:42:41.000000000 +0300
+++ linux-4.9.y/net/ipv4/ip_output.c	2021-06-07 13:01:34.000000000 +0300
@@ -1260,7 +1260,7 @@
 		if (skb->ip_summed != CHECKSUM_PARTIAL)
 			return -EOPNOTSUPP;
 
-		skb_shinfo(skb)->gso_size = mtu - fragheaderlen;
+		skb_shinfo(skb)->gso_size = maxfraglen - fragheaderlen;
 		skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
 	}
 	cork->length += size;