diff --git a/p4src/checksum_diff.p4 b/p4src/checksum_diff.p4
index e586d65..ab6b503 100644
--- a/p4src/checksum_diff.p4
+++ b/p4src/checksum_diff.p4
@@ -197,14 +197,24 @@ control MyIngress(inout headers hdr,
                     v4sum();
                     v6sum();
                     bit<16> diff = meta.v6sum - meta.v4sum;
-                    hdr.udp.checksum = hdr.udp.checksum + ~diff;
+                    hdr.udp.checksum = hdr.udp.checksum + ~diff +1;
+//                    hdr.udp.checksum = ~diff;
 
                     #else
                     meta.chk_udp_v6 = 1;
                     #endif
                 }
                 if(hdr.tcp.isValid()) {
+                    #ifdef USE_NICO_DELTA_CHECKSUM
+                    v4sum();
+                    v6sum();
+                    bit<16> diff = meta.v6sum - meta.v4sum;
+                    hdr.tcp.checksum = hdr.tcp.checksum + ~diff;
+
+                    #else
+
                     meta.chk_tcp_v6 = 1;
+                    #endif
                 }
 
                 v6_networks.apply();