diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 896ce3f..4e9c74b 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -577,15 +577,16 @@
 			goto drop_nolock;
 
 		if (flags&GRE_CSUM) {
-			if (skb->ip_summed == CHECKSUM_HW) {
+			switch (skb->ip_summed) {
+			case CHECKSUM_HW:
 				csum = (u16)csum_fold(skb->csum);
-				if (csum)
-					skb->ip_summed = CHECKSUM_NONE;
-			}
-			if (skb->ip_summed == CHECKSUM_NONE) {
-				skb->csum = skb_checksum(skb, 0, skb->len, 0);
+				if (!csum)
+					break;
+				/* fall through */
+			case CHECKSUM_NONE:
+				skb->csum = 0;
+				csum = __skb_checksum_complete(skb);
 				skb->ip_summed = CHECKSUM_HW;
-				csum = (u16)csum_fold(skb->csum);
 			}
 			offset += 4;
 		}