diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index ec2ab82d0d4b02a8f92f0d4ec85fab0c3a7f639f..42f6027e30b450dd30cda31fb1f9d0b3173bbbef 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1270,6 +1270,20 @@ static void udp_set_dev_scratch(struct sk_buff *skb)
 		scratch->_tsize_state |= UDP_SKB_IS_STATELESS;
 }
 
+static void udp_skb_csum_unnecessary_set(struct sk_buff *skb)
+{
+	/* We come here after udp_lib_checksum_complete() returned 0.
+	 * This means that __skb_checksum_complete() might have
+	 * set skb->csum_valid to 1.
+	 * On 64bit platforms, we can set csum_unnecessary
+	 * to true, but only if the skb is not shared.
+	 */
+#if BITS_PER_LONG == 64
+	if (!skb_shared(skb))
+		udp_skb_scratch(skb)->csum_unnecessary = true;
+#endif
+}
+
 static int udp_skb_truesize(struct sk_buff *skb)
 {
 	return udp_skb_scratch(skb)->_tsize_state & ~UDP_SKB_IS_STATELESS;
@@ -1504,10 +1518,7 @@ static struct sk_buff *__first_packet_length(struct sock *sk,
 			*total += skb->truesize;
 			kfree_skb(skb);
 		} else {
-			/* the csum related bits could be changed, refresh
-			 * the scratch area
-			 */
-			udp_set_dev_scratch(skb);
+			udp_skb_csum_unnecessary_set(skb);
 			break;
 		}
 	}