diff --git a/CHANGELOG b/CHANGELOG
index 6bd40390..fc854970 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -424,6 +424,10 @@ HISTORY
 
   ++ Bug fixes:
 
+  2007-10-07 Simon Goldschmidt
+  * udp.c, inet.c, inet.h: Fixed UDPLite SENDING: Checksum was always generated
+    too short and also was generated wrong if checksum coverage != tot_len.
+
   2007-10-07 Frédéric Bernon
   * sockets.c, api.h, api_lib.c: First step to fix "bug #20900 : Potential
     crash error problem with netconn_peer & netconn_addr". VERY IMPORTANT:
diff --git a/src/core/inet.c b/src/core/inet.c
index 76fa356f..38a686a1 100644
--- a/src/core/inet.c
+++ b/src/core/inet.c
@@ -294,6 +294,69 @@ inet_chksum_pseudo(struct pbuf *p,
   return (u16_t)~(acc & 0xffffUL);
 }
 
+/* inet_chksum_pseudo:
+ *
+ * Calculates the pseudo Internet checksum used by TCP and UDP for a pbuf chain.
+ * IP addresses are expected to be in network byte order.
+ *
+ * @param p chain of pbufs over that a checksum should be calculated (ip data part)
+ * @param src source ip address (used for checksum of pseudo header)
+ * @param dst destination ip address (used for checksum of pseudo header)
+ * @param proto ip protocol (used for checksum of pseudo header)
+ * @param proto_len length of the ip data part (used for checksum of pseudo header)
+ * @return checksum (as u16_t) to be saved directly in the protocol header
+ */
+u16_t
+inet_chksum_pseudo_partial(struct pbuf *p,
+       struct ip_addr *src, struct ip_addr *dest,
+       u8_t proto, u16_t proto_len, u16_t chksum_len)
+{
+  u32_t acc;
+  struct pbuf *q;
+  u8_t swapped;
+  u16_t chklen;
+
+  acc = 0;
+  swapped = 0;
+  /* iterate through all pbuf in chain */
+  for(q = p; (q != NULL) && (chksum_len > 0); q = q->next) {
+    LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): checksumming pbuf %p (has next %p) \n",
+      (void *)q, (void *)q->next));
+    chklen = q->len;
+    if (chklen > chksum_len) {
+      chklen = chksum_len;
+    }
+    acc += LWIP_CHKSUM(q->payload, chklen);
+    chksum_len -= chklen;
+    LWIP_ASSERT("delete me", chksum_len < 0x7fff);
+    /*LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): unwrapped lwip_chksum()=%"X32_F" \n", acc));*/
+    while ((acc >> 16) != 0) {
+      acc = (acc & 0xffffUL) + (acc >> 16);
+    }
+    if (q->len % 2 != 0) {
+      swapped = 1 - swapped;
+      acc = ((acc & 0xff) << 8) | ((acc & 0xff00UL) >> 8);
+    }
+    /*LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): wrapped lwip_chksum()=%"X32_F" \n", acc));*/
+  }
+
+  if (swapped) {
+    acc = ((acc & 0xff) << 8) | ((acc & 0xff00UL) >> 8);
+  }
+  acc += (src->addr & 0xffffUL);
+  acc += ((src->addr >> 16) & 0xffffUL);
+  acc += (dest->addr & 0xffffUL);
+  acc += ((dest->addr >> 16) & 0xffffUL);
+  acc += (u32_t)htons((u16_t)proto);
+  acc += (u32_t)htons(proto_len);
+
+  while ((acc >> 16) != 0) {
+    acc = (acc & 0xffffUL) + (acc >> 16);
+  }
+  LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): pbuf chain lwip_chksum()=%"X32_F"\n", acc));
+  return (u16_t)~(acc & 0xffffUL);
+}
+
 /* inet_chksum:
  *
  * Calculates the Internet checksum over a portion of memory. Used primarily for IP
diff --git a/src/core/udp.c b/src/core/udp.c
index 4b102b87..e0c472b8 100644
--- a/src/core/udp.c
+++ b/src/core/udp.c
@@ -39,10 +39,13 @@
 
 /* udp.c
  *
- * The code for the User Datagram Protocol UDP.
+ * The code for the User Datagram Protocol UDP & UDPLite (RFC 3828).
  *
  */
 
+/* @todo Check the use of '(struct udp_pcb).chksum_len_rx'!
+ */
+
 #include "lwip/opt.h"
 
 #if LWIP_UDP /* don't build if not configured for use in lwipopts.h */
@@ -425,11 +428,11 @@ udp_send(struct udp_pcb *pcb, struct pbuf *p)
 #if LWIP_UDPLITE
   /* UDP Lite protocol? */
   if (pcb->flags & UDP_FLAGS_UDPLITE) {
-    u16_t chklen;
+    u16_t chklen, chklen_hdr;
     LWIP_DEBUGF(UDP_DEBUG, ("udp_send: UDP LITE packet length %"U16_F"\n", q->tot_len));
     /* set UDP message length in UDP header */
-    chklen = pcb->chksum_len_rx;
-    if (chklen < sizeof(struct udp_hdr)) {
+    chklen_hdr = chklen = pcb->chksum_len_tx;
+    if ((chklen < sizeof(struct udp_hdr)) || (chklen > q->tot_len)) {
       if (chklen != 0) {
         LWIP_DEBUGF(UDP_DEBUG, ("udp_send: UDP LITE pcb->chksum_len is illegal: %"U16_F"\n", chklen));
       }
@@ -439,13 +442,14 @@ udp_send(struct udp_pcb *pcb, struct pbuf *p)
          checksum, therefore, if chksum_len has an illegal
          value, we generate the checksum over the complete
          packet to be safe. */
-      chklen = p->tot_len;
+      chklen_hdr = 0;
+      chklen = q->tot_len;
     }
-    udphdr->len = htons(chklen);
+    udphdr->len = htons(chklen_hdr);
     /* calculate checksum */
 #if CHECKSUM_GEN_UDP
-    udphdr->chksum = inet_chksum_pseudo(q, src_ip, &(pcb->remote_ip),
-                                        IP_PROTO_UDP, chklen);
+    udphdr->chksum = inet_chksum_pseudo_partial(q, src_ip, &(pcb->remote_ip),
+                                        IP_PROTO_UDPLITE, q->tot_len, chklen);
     /* chksum zero must become 0xffff, as zero means 'no checksum' */
     if (udphdr->chksum == 0x0000)
       udphdr->chksum = 0xffff;
diff --git a/src/include/ipv4/lwip/inet.h b/src/include/ipv4/lwip/inet.h
index 6dfad143..ccf69588 100644
--- a/src/include/ipv4/lwip/inet.h
+++ b/src/include/ipv4/lwip/inet.h
@@ -49,6 +49,9 @@ u16_t inet_chksum_pbuf(struct pbuf *p);
 u16_t inet_chksum_pseudo(struct pbuf *p,
        struct ip_addr *src, struct ip_addr *dest,
        u8_t proto, u16_t proto_len);
+u16_t inet_chksum_pseudo_partial(struct pbuf *p,
+       struct ip_addr *src, struct ip_addr *dest,
+       u8_t proto, u16_t proto_len, u16_t chksum_len);
 
 u32_t inet_addr(const char *cp);
 int inet_aton(const char *cp, struct in_addr *addr);