diff --git a/doc/plan.org b/doc/plan.org
index 06bcfbc..362e56e 100644
--- a/doc/plan.org
+++ b/doc/plan.org
@@ -5620,7 +5620,19 @@ bit<16> ones_complement_sum(in bit<16> x, in bit<16> y) {
 }
 
 #+END_CENTER
-*** TODO 2019-07-17: use 17 bits for addition -> totally off!x
+*** DONE 2019-07-17: use 17 bits for addition -> totally off!x
+    CLOSED: [2019-07-17 Wed 18:03]
+*** DONE 2019-07-17: retest checksumming: of tcp/udp to V6: ok!
+    CLOSED: [2019-07-17 Wed 18:03]
+PCAP files to prove it works:
+#+BEGIN_CENTER
+ create mode 100644 pcap/tcp-udp-delta-2019-07-17-1555-h1.pcap
+ create mode 100644 pcap/tcp-udp-delta-2019-07-17-1555-h3.pcap
+ create mode 100644 pcap/tcp-udp-delta-2019-07-17-1557-h1.pcap
+ create mode 100644 pcap/tcp-udp-delta-2019-07-17-1558-h3.pcap
+
+#+END_CENTER
+***
 ** The NetPFGA saga
 Problems encountered:
 - The logfile for a compile run is 10k+ lines
diff --git a/p4src/actions_delta_checksum.p4 b/p4src/actions_delta_checksum.p4
index 751f7f8..c705e19 100644
--- a/p4src/actions_delta_checksum.p4
+++ b/p4src/actions_delta_checksum.p4
@@ -70,6 +70,24 @@ action delta_udp_from_v4_to_v6()
     hdr.udp.checksum = (bit<16>) tmp;
 }
 
+action delta_udp_from_v6_to_v4()
+{
+    delta_prepare();
+
+    bit<17> tmp = (bit<17>) hdr.udp.checksum + (bit<17>) meta.v4sum;
+    if (tmp[16:16] == 1) {
+        tmp = tmp + 1;
+        tmp[16:16] = 0;
+    }
+    tmp = tmp + (bit<17>) (0xffff - meta.v6sum);
+    if (tmp[16:16] == 1) {
+        tmp = tmp + 1;
+        tmp[16:16] = 0;
+    }
+
+    hdr.udp.checksum = (bit<16>) tmp;
+}
+
 action delta_tcp_from_v4_to_v6()
 {
     delta_prepare();
@@ -88,6 +106,24 @@ action delta_tcp_from_v4_to_v6()
     hdr.tcp.checksum = (bit<16>) tmp;
 }
 
+action delta_tcp_from_v6_to_v4()
+{
+    delta_prepare();
+
+    bit<17> tmp = (bit<17>) hdr.tcp.checksum + (bit<17>) meta.v4sum;
+    if (tmp[16:16] == 1) {
+        tmp = tmp + 1;
+        tmp[16:16] = 0;
+    }
+    tmp = tmp + (bit<17>) (0xffff - meta.v6sum);
+    if (tmp[16:16] == 1) {
+        tmp = tmp + 1;
+        tmp[16:16] = 0;
+    }
+
+    hdr.tcp.checksum = (bit<16>) tmp;
+}
+
 action delta_ipv4_from_v6_to_v4()
 {
     bit<16> tmp = 0;
diff --git a/p4src/checksum_diff.p4 b/p4src/checksum_diff.p4
index b49bd96..39d40b9 100644
--- a/p4src/checksum_diff.p4
+++ b/p4src/checksum_diff.p4
@@ -55,10 +55,19 @@ control MyIngress(inout headers hdr,
                     }
                 }
                 if(hdr.udp.isValid()) {
+                    #ifdef USE_NICO_DELTA_CHECKSUM
+                    delta_udp_from_v6_to_v4();
+                    #else
                     meta.chk_udp_v4 = 1;
+                    #endif
                 }
                 if(hdr.tcp.isValid()) {
+                    #ifdef USE_NICO_DELTA_CHECKSUM
+                    delta_tcp_from_v6_to_v4();
+                    #else
+
                     meta.chk_tcp_v4 = 1;
+                    #endif
                 }
 
                 v4_networks.apply();       /* apply egress for IPv4 */