diff --git a/src/vnet/devices/virtio/node.c b/src/vnet/devices/virtio/node.c
index e9c72eb..ba17075 100644
--- a/src/vnet/devices/virtio/node.c
+++ b/src/vnet/devices/virtio/node.c
@@ -142,10 +142,12 @@
 }
 
 static_always_inline void
-fill_gso_buffer_flags (vlib_buffer_t * b0, struct virtio_net_hdr_v1 *hdr)
+virtio_needs_csum (vlib_buffer_t * b0, struct virtio_net_hdr_v1 *hdr,
+		   u8 * l4_proto, u8 * l4_hdr_sz)
 {
-  u8 l4_proto = 0;
-  u8 l4_hdr_sz = 0;
+  *l4_proto = 0;
+  *l4_hdr_sz = 0;
+
   if (hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM)
 
     {
@@ -175,7 +177,7 @@
 	  ip4_header_t *ip4 =
 	    (ip4_header_t *) (vlib_buffer_get_current (b0) + l2hdr_sz);
 	  vnet_buffer (b0)->l4_hdr_offset = l2hdr_sz + ip4_header_bytes (ip4);
-	  l4_proto = ip4->protocol;
+	  *l4_proto = ip4->protocol;
 	  b0->flags |=
 	    (VNET_BUFFER_F_IS_IP4 | VNET_BUFFER_F_OFFLOAD_IP_CKSUM);
 	  b0->flags |=
@@ -189,32 +191,38 @@
 	    (ip6_header_t *) (vlib_buffer_get_current (b0) + l2hdr_sz);
 	  vnet_buffer (b0)->l4_hdr_offset = l2hdr_sz + sizeof (ip6_header_t);
 	  /* FIXME IPv6 EH traversal */
-	  l4_proto = ip6->protocol;
+	  *l4_proto = ip6->protocol;
 	  b0->flags |= (VNET_BUFFER_F_IS_IP6 |
 			VNET_BUFFER_F_L2_HDR_OFFSET_VALID
 			| VNET_BUFFER_F_L3_HDR_OFFSET_VALID |
 			VNET_BUFFER_F_L4_HDR_OFFSET_VALID);
 	}
-      if (l4_proto == IP_PROTOCOL_TCP)
+      if (*l4_proto == IP_PROTOCOL_TCP)
 	{
 	  b0->flags |= VNET_BUFFER_F_OFFLOAD_TCP_CKSUM;
 	  tcp_header_t *tcp = (tcp_header_t *) (vlib_buffer_get_current (b0) +
 						vnet_buffer
 						(b0)->l4_hdr_offset);
-	  l4_hdr_sz = tcp_header_bytes (tcp);
+	  *l4_hdr_sz = tcp_header_bytes (tcp);
 	  tcp->checksum = 0;
 	}
-      else if (l4_proto == IP_PROTOCOL_UDP)
+      else if (*l4_proto == IP_PROTOCOL_UDP)
 	{
 	  b0->flags |= VNET_BUFFER_F_OFFLOAD_UDP_CKSUM;
 	  udp_header_t *udp = (udp_header_t *) (vlib_buffer_get_current (b0) +
 						vnet_buffer
 						(b0)->l4_hdr_offset);
-	  l4_hdr_sz = sizeof (*udp);
+	  *l4_hdr_sz = sizeof (*udp);
 	  udp->checksum = 0;
 	}
     }
 
+}
+
+static_always_inline void
+fill_gso_buffer_flags (vlib_buffer_t * b0, struct virtio_net_hdr_v1 *hdr,
+		       u8 l4_proto, u8 l4_hdr_sz)
+{
   if (hdr->gso_type == VIRTIO_NET_HDR_GSO_TCPV4)
     {
       ASSERT (hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM);
@@ -264,6 +272,7 @@
 
       while (n_left && n_left_to_next)
 	{
+	  u8 l4_proto, l4_hdr_sz;
 	  u16 num_buffers = 1;
 	  struct vring_used_elem *e = &vring->used->ring[last & mask];
 	  struct virtio_net_hdr_v1 *hdr;
@@ -280,8 +289,10 @@
 	  b0->total_length_not_including_first_buffer = 0;
 	  b0->flags = VLIB_BUFFER_TOTAL_LENGTH_VALID;
 
+	  virtio_needs_csum (b0, hdr, &l4_proto, &l4_hdr_sz);
+
 	  if (gso_enabled)
-	    fill_gso_buffer_flags (b0, hdr);
+	    fill_gso_buffer_flags (b0, hdr, l4_proto, l4_hdr_sz);
 
 	  vnet_buffer (b0)->sw_if_index[VLIB_RX] = vif->sw_if_index;
 	  vnet_buffer (b0)->sw_if_index[VLIB_TX] = (u32) ~ 0;