diff --git a/checksum.c b/checksum.c
index 14b7113..a4dc9b8 100644
--- a/checksum.c
+++ b/checksum.c
@@ -28,12 +28,12 @@
 
 /* function: ip_checksum_add
  * adds data to a checksum
- * current_sum - the current checksum (or 0 to start a new checksum)
+ * current - the current checksum (or 0 to start a new checksum)
  * data        - the data to add to the checksum
  * len         - length of data
  */
-uint32_t ip_checksum_add(uint32_t current_sum, const void *data, int len) {
-  uint32_t checksum = current_sum;
+uint32_t ip_checksum_add(uint32_t current, const void *data, int len) {
+  uint32_t checksum = current;
   int left = len;
   const uint16_t *data_16 = data;
 
@@ -76,38 +76,40 @@
 
 /* function: ipv6_pseudo_header_checksum
  * calculate the pseudo header checksum for use in tcp/udp/icmp headers
- * current_sum - the current checksum or 0 to start a new checksum
- * ip6         - the ipv6 header
+ * current - the current checksum or 0 to start a new checksum
+ * ip6     - the ipv6 header
+ * len     - the transport length (transport header + payload)
  */
-uint32_t ipv6_pseudo_header_checksum(uint32_t current_sum, const struct ip6_hdr *ip6) {
+uint32_t ipv6_pseudo_header_checksum(uint32_t current, const struct ip6_hdr *ip6, uint16_t len) {
   uint32_t checksum_len, checksum_next;
 
-  checksum_len = htonl(ntohs(ip6->ip6_plen));
+  checksum_len = htonl((uint32_t) len);
   checksum_next = htonl(ip6->ip6_nxt);
 
-  current_sum = ip_checksum_add(current_sum,&(ip6->ip6_src),sizeof(struct in6_addr));
-  current_sum = ip_checksum_add(current_sum,&(ip6->ip6_dst),sizeof(struct in6_addr));
-  current_sum = ip_checksum_add(current_sum,&checksum_len,sizeof(checksum_len));
-  current_sum = ip_checksum_add(current_sum,&checksum_next,sizeof(checksum_next));
+  current = ip_checksum_add(current, &(ip6->ip6_src), sizeof(struct in6_addr));
+  current = ip_checksum_add(current, &(ip6->ip6_dst), sizeof(struct in6_addr));
+  current = ip_checksum_add(current, &checksum_len, sizeof(checksum_len));
+  current = ip_checksum_add(current, &checksum_next, sizeof(checksum_next));
 
-  return current_sum;
+  return current;
 }
 
 /* function: ipv4_pseudo_header_checksum
  * calculate the pseudo header checksum for use in tcp/udp headers
- * current_sum - the current checksum or 0 to start a new checksum
- * ip          - the ipv4 header
+ * current - the current checksum or 0 to start a new checksum
+ * ip      - the ipv4 header
+ * len     - the transport length (transport header + payload)
  */
-uint32_t ipv4_pseudo_header_checksum(uint32_t current_sum, const struct iphdr *ip) {
+uint32_t ipv4_pseudo_header_checksum(uint32_t current, const struct iphdr *ip, uint16_t len) {
   uint16_t temp_protocol, temp_length;
 
   temp_protocol = htons(ip->protocol);
-  temp_length = htons(ntohs(ip->tot_len) - ip->ihl*4);
+  temp_length = htons(len);
 
-  current_sum = ip_checksum_add(current_sum, &(ip->saddr), sizeof(uint32_t));
-  current_sum = ip_checksum_add(current_sum, &(ip->daddr), sizeof(uint32_t));
-  current_sum = ip_checksum_add(current_sum, &temp_protocol, sizeof(uint16_t));
-  current_sum = ip_checksum_add(current_sum, &temp_length, sizeof(uint16_t));
+  current = ip_checksum_add(current, &(ip->saddr), sizeof(uint32_t));
+  current = ip_checksum_add(current, &(ip->daddr), sizeof(uint32_t));
+  current = ip_checksum_add(current, &temp_protocol, sizeof(uint16_t));
+  current = ip_checksum_add(current, &temp_length, sizeof(uint16_t));
 
-  return current_sum;
+  return current;
 }
diff --git a/checksum.h b/checksum.h
index c8346a0..473f5f5 100644
--- a/checksum.h
+++ b/checksum.h
@@ -18,11 +18,11 @@
 #ifndef __CHECKSUM_H__
 #define __CHECKSUM_H__
 
-uint32_t ip_checksum_add(uint32_t current_sum, const void *data, int len);
+uint32_t ip_checksum_add(uint32_t current, const void *data, int len);
 uint16_t ip_checksum_finish(uint32_t temp_sum);
 uint16_t ip_checksum(const void *data, int len);
 
-uint32_t ipv6_pseudo_header_checksum(uint32_t current_sum, const struct ip6_hdr *ip6);
-uint32_t ipv4_pseudo_header_checksum(uint32_t current_sum, const struct iphdr *ip);
+uint32_t ipv6_pseudo_header_checksum(uint32_t current, const struct ip6_hdr *ip6, uint16_t len);
+uint32_t ipv4_pseudo_header_checksum(uint32_t current, const struct iphdr *ip, uint16_t len);
 
 #endif /* __CHECKSUM_H__ */
diff --git a/dump.c b/dump.c
index e538f3e..fe9721a 100644
--- a/dump.c
+++ b/dump.c
@@ -146,14 +146,14 @@
 /* print ipv4/udp header */
 void dump_udp(const struct udphdr *udp, const struct iphdr *ip, const char *payload, size_t payload_size) {
   uint32_t temp_checksum;
-  temp_checksum = ipv4_pseudo_header_checksum(0, ip);
+  temp_checksum = ipv4_pseudo_header_checksum(0, ip, sizeof(*udp) + payload_size);
   dump_udp_generic(udp, temp_checksum, payload, payload_size);
 }
 
 /* print ipv6/udp header */
 void dump_udp6(const struct udphdr *udp, const struct ip6_hdr *ip6, const char *payload, size_t payload_size) {
   uint32_t temp_checksum;
-  temp_checksum = ipv6_pseudo_header_checksum(0, ip6);
+  temp_checksum = ipv6_pseudo_header_checksum(0, ip6, sizeof(*udp) + payload_size);
   dump_udp_generic(udp, temp_checksum, payload, payload_size);
 }
 
@@ -202,7 +202,7 @@
 void dump_tcp(const struct tcphdr *tcp, const struct iphdr *ip, const char *payload, size_t payload_size, const char *options, size_t options_size) {
   uint32_t temp_checksum;
 
-  temp_checksum = ipv4_pseudo_header_checksum(0, ip);
+  temp_checksum = ipv4_pseudo_header_checksum(0, ip, sizeof(*tcp) + options_size + payload_size);
   dump_tcp_generic(tcp, options, options_size, temp_checksum, payload, payload_size);
 }
 
@@ -210,7 +210,7 @@
 void dump_tcp6(const struct tcphdr *tcp, const struct ip6_hdr *ip6, const char *payload, size_t payload_size, const char *options, size_t options_size) {
   uint32_t temp_checksum;
 
-  temp_checksum = ipv6_pseudo_header_checksum(0, ip6);
+  temp_checksum = ipv6_pseudo_header_checksum(0, ip6, sizeof(*tcp) + options_size + payload_size);
   dump_tcp_generic(tcp, options, options_size, temp_checksum, payload, payload_size);
 }
 
diff --git a/translate.c b/translate.c
index cdaca14..89a7e7b 100644
--- a/translate.c
+++ b/translate.c
@@ -142,7 +142,7 @@
   icmp6_targ.icmp6_id = icmp->un.echo.id;
   icmp6_targ.icmp6_seq = icmp->un.echo.sequence;
 
-  checksum_temp = ipv6_pseudo_header_checksum(0,&ip6_targ);
+  checksum_temp = ipv6_pseudo_header_checksum(0, &ip6_targ, sizeof(icmp6_targ) + payload_size);
   checksum_temp = ip_checksum_add(checksum_temp, &icmp6_targ, sizeof(icmp6_targ));
   checksum_temp = ip_checksum_add(checksum_temp, payload, payload_size);
   icmp6_targ.icmp6_cksum = ip_checksum_finish(checksum_temp);
@@ -255,7 +255,7 @@
 
   fill_ip6_header(&ip6_targ,payload_size + sizeof(struct udphdr),IPPROTO_UDP,ip);
 
-  checksum = ipv6_pseudo_header_checksum(0, &ip6_targ);
+  checksum = ipv6_pseudo_header_checksum(0, &ip6_targ, sizeof(*udp) + payload_size);
 
   io_targ[0].iov_base = &tun_header;
   io_targ[0].iov_len = sizeof(tun_header);
@@ -283,7 +283,7 @@
 
   fill_ip_header(&ip_targ,payload_size + sizeof(struct udphdr),IPPROTO_UDP,ip6);
 
-  checksum = ipv4_pseudo_header_checksum(0, &ip_targ);
+  checksum = ipv4_pseudo_header_checksum(0, &ip_targ, sizeof(*udp) + payload_size);
 
   io_targ[0].iov_base = &tun_header;
   io_targ[0].iov_len = sizeof(tun_header);
@@ -363,7 +363,7 @@
 
   fill_ip6_header(&ip6_targ,payload_size+options_size+sizeof(struct tcphdr),IPPROTO_TCP,ip);
 
-  checksum = ipv6_pseudo_header_checksum(0, &ip6_targ);
+  checksum = ipv6_pseudo_header_checksum(0, &ip6_targ, sizeof(*tcp) + options_size + payload_size);
 
   io_targ[0].iov_base = &tun_header;
   io_targ[0].iov_len = sizeof(tun_header);
@@ -393,7 +393,7 @@
 
   fill_ip_header(&ip_targ,payload_size+options_size+sizeof(struct tcphdr),IPPROTO_TCP,ip6);
 
-  checksum = ipv4_pseudo_header_checksum(0, &ip_targ);
+  checksum = ipv4_pseudo_header_checksum(0, &ip_targ, sizeof(*tcp) + payload_size + options_size);
 
   io_targ[0].iov_base = &tun_header;
   io_targ[0].iov_len = sizeof(tun_header);