diff --git a/CHANGELOG b/CHANGELOG
index 3188dc5a..8f0f5ba3 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -13,6 +13,10 @@ HISTORY
 
   ++ New features:
 
+  2010-05-02: Simon Goldschmidt
+  * netbuf.h/.c, sockets.c, api_msg.c: use checksum-on-copy for sending
+    UDP data for LWIP_NETIF_TX_SINGLE_PBUF==1
+
   2010-04-30: Simon Goldschmidt
   * udp.h/.c, pbuf.h/.c: task #6849: added udp_send(_to/_if) functions that
     take a precalculated checksum, added pbuf_fill_chksum() to copy data
diff --git a/src/api/api_msg.c b/src/api/api_msg.c
index 2ebe730d..36d25573 100644
--- a/src/api/api_msg.c
+++ b/src/api/api_msg.c
@@ -180,8 +180,11 @@ recv_udp(void *arg, struct udp_pcb *pcb, struct pbuf *p,
       const struct ip_hdr* iphdr = ip_current_header();
       /* get the UDP header - always in the first pbuf, ensured by udp_input */
       const struct udp_hdr* udphdr = (void*)(((char*)iphdr) + IPH_LEN(iphdr));
+#if LWIP_CHECKSUM_ON_COPY
+      buf->flags = NETBUF_FLAG_DESTADDR;
+#endif /* LWIP_CHECKSUM_ON_COPY */
       buf->toaddr = (ip_addr_t*)&iphdr->dest;
-      buf->toport = udphdr->dest;
+      buf->toport_chksum = udphdr->dest;
     }
 #endif /* LWIP_NETBUF_RECVINFO */
   }
@@ -1091,11 +1094,22 @@ do_send(struct api_msg_msg *msg)
 #endif
 #if LWIP_UDP
       case NETCONN_UDP:
+#if LWIP_CHECKSUM_ON_COPY
+        if (msg->msg.b->addr == NULL) {
+          msg->err = udp_send_chksum(msg->conn->pcb.udp, msg->msg.b->p,
+            msg->msg.b->flags & NETBUF_FLAG_CHKSUM, msg->msg.b->toport_chksum);
+        } else {
+          msg->err = udp_sendto_chksum(msg->conn->pcb.udp, msg->msg.b->p,
+            msg->msg.b->addr, msg->msg.b->port,
+            msg->msg.b->flags & NETBUF_FLAG_CHKSUM, msg->msg.b->toport_chksum);
+        }
+#else /* LWIP_CHECKSUM_ON_COPY */
         if (msg->msg.b->addr == NULL) {
           msg->err = udp_send(msg->conn->pcb.udp, msg->msg.b->p);
         } else {
           msg->err = udp_sendto(msg->conn->pcb.udp, msg->msg.b->p, msg->msg.b->addr, msg->msg.b->port);
         }
+#endif /* LWIP_CHECKSUM_ON_COPY */
         break;
 #endif /* LWIP_UDP */
       default:
diff --git a/src/api/netbuf.c b/src/api/netbuf.c
index f6c898fd..d2d2e42e 100644
--- a/src/api/netbuf.c
+++ b/src/api/netbuf.c
@@ -63,10 +63,15 @@ netbuf *netbuf_new(void)
     buf->ptr = NULL;
     buf->addr = NULL;
     buf->port = 0;
+#if LWIP_NETBUF_RECVINFO || LWIP_CHECKSUM_ON_COPY
+#if LWIP_CHECKSUM_ON_COPY
+    buf->flags = 0;
+#endif /* LWIP_CHECKSUM_ON_COPY */
+    buf->toport_chksum = 0;
 #if LWIP_NETBUF_RECVINFO
     buf->toaddr = NULL;
-    buf->toport = 0;
 #endif /* LWIP_NETBUF_RECVINFO */
+#endif /* LWIP_NETBUF_RECVINFO || LWIP_CHECKSUM_ON_COPY */
     return buf;
   } else {
     return NULL;
diff --git a/src/api/sockets.c b/src/api/sockets.c
index 386d5d7e..8d9adb34 100644
--- a/src/api/sockets.c
+++ b/src/api/sockets.c
@@ -52,6 +52,9 @@
 #include "lwip/udp.h"
 #include "lwip/tcpip.h"
 #include "lwip/pbuf.h"
+#if LWIP_CHECKSUM_ON_COPY
+#include "lwip/inet_chksum.h"
+#endif
 
 #include <string.h>
 
@@ -823,6 +826,12 @@ lwip_sendto(int s, const void *data, size_t size, int flags,
 #if LWIP_NETIF_TX_SINGLE_PBUF
     p = pbuf_alloc(PBUF_TRANSPORT, short_size, PBUF_RAM);
     if (p != NULL) {
+#if LWIP_CHECKSUM_ON_COPY
+      u16_t chksum = 0;
+      if (sock->conn->type != NETCONN_RAW) {
+        chksum = LWIP_CHKSUM_COPY(p->payload, data, short_size);
+      } else
+#endif /* LWIP_CHECKSUM_ON_COPY */
       MEMCPY(p->payload, data, size);
 #else /* LWIP_NETIF_TX_SINGLE_PBUF */
     p = pbuf_alloc(PBUF_TRANSPORT, short_size, PBUF_REF);
@@ -836,7 +845,13 @@ lwip_sendto(int s, const void *data, size_t size, int flags,
       if (sock->conn->type == NETCONN_RAW) {
         err = sock->conn->last_err = raw_sendto(sock->conn->pcb.raw, p, &remote_addr);
       } else {
-        err = sock->conn->last_err = udp_sendto(sock->conn->pcb.udp, p, &remote_addr, ntohs(to_in->sin_port));
+#if LWIP_CHECKSUM_ON_COPY && LWIP_NETIF_TX_SINGLE_PBUF
+        err = sock->conn->last_err = udp_sendto_chksum(sock->conn->pcb.udp, p,
+          &remote_addr, ntohs(to_in->sin_port), 1, chksum);
+#else /* LWIP_CHECKSUM_ON_COPY && LWIP_NETIF_TX_SINGLE_PBUF */
+        err = sock->conn->last_err = udp_sendto(sock->conn->pcb.udp, p,
+          &remote_addr, ntohs(to_in->sin_port));
+#endif /* LWIP_CHECKSUM_ON_COPY && LWIP_NETIF_TX_SINGLE_PBUF */
       }
       UNLOCK_TCPIP_CORE();
       
@@ -848,16 +863,19 @@ lwip_sendto(int s, const void *data, size_t size, int flags,
 #else
   /* initialize a buffer */
   buf.p = buf.ptr = NULL;
+#if LWIP_CHECKSUM_ON_COPY
+  buf.flags = 0;
+#endif /* LWIP_CHECKSUM_ON_COPY */
   if (to) {
     inet_addr_to_ipaddr(&remote_addr, &to_in->sin_addr);
-    remote_port      = ntohs(to_in->sin_port);
-    buf.addr         = &remote_addr;
-    buf.port         = remote_port;
+    remote_port           = ntohs(to_in->sin_port);
+    netbuf_fromaddr(&buf) = &remote_addr;
+    netbuf_fromport(&buf) = remote_port;
   } else {
     ip_addr_set_zero(&remote_addr);
-    remote_port      = 0;
-    buf.addr         = NULL;
-    buf.port         = 0;
+    remote_port           = 0;
+    netbuf_fromaddr(&buf) = NULL;
+    netbuf_fromport(&buf) = 0;
   }
 
   LWIP_DEBUGF(SOCKETS_DEBUG, ("lwip_sendto(%d, data=%p, short_size=%d"U16_F", flags=0x%x to=",
@@ -871,7 +889,16 @@ lwip_sendto(int s, const void *data, size_t size, int flags,
   if (netbuf_alloc(&buf, short_size) == NULL) {
     err = ERR_MEM;
   } else {
-    err = netbuf_take(&buf, data, short_size);
+#if LWIP_CHECKSUM_ON_COPY
+    if (sock->conn->type != NETCONN_RAW) {
+      u16_t chksum = LWIP_CHKSUM_COPY(buf.p->payload, data, short_size);
+      netbuf_set_chksum(&buf, chksum);
+      err = ERR_OK;
+    } else
+#endif /* LWIP_CHECKSUM_ON_COPY */
+    {
+      err = netbuf_take(&buf, data, short_size);
+    }
   }
 #else /* LWIP_NETIF_TX_SINGLE_PBUF */
   err = netbuf_ref(&buf, data, short_size);
diff --git a/src/include/lwip/netbuf.h b/src/include/lwip/netbuf.h
index 86e4f1d3..d6f2655a 100644
--- a/src/include/lwip/netbuf.h
+++ b/src/include/lwip/netbuf.h
@@ -40,14 +40,24 @@
 extern "C" {
 #endif
 
+/** This netbuf has dest-addr/port set */
+#define NETBUF_FLAG_DESTADDR    0x01
+/** This netbuf includes a checksum */
+#define NETBUF_FLAG_CHKSUM      0x02
+
 struct netbuf {
   struct pbuf *p, *ptr;
   ip_addr_t *addr;
   u16_t port;
+#if LWIP_NETBUF_RECVINFO || LWIP_CHECKSUM_ON_COPY
+#if LWIP_CHECKSUM_ON_COPY
+  u8_t flags;
+#endif /* LWIP_CHECKSUM_ON_COPY */
+  u16_t toport_chksum;
 #if LWIP_NETBUF_RECVINFO
-  u16_t toport;
   ip_addr_t *toaddr;
 #endif /* LWIP_NETBUF_RECVINFO */
+#endif /* LWIP_NETBUF_RECVINFO || LWIP_CHECKSUM_ON_COPY */
 };
 
 /* Network buffer functions: */
@@ -56,12 +66,12 @@ void              netbuf_delete   (struct netbuf *buf);
 void *            netbuf_alloc    (struct netbuf *buf, u16_t size);
 void              netbuf_free     (struct netbuf *buf);
 err_t             netbuf_ref      (struct netbuf *buf,
-           const void *dataptr, u16_t size);
+                                   const void *dataptr, u16_t size);
 void              netbuf_chain    (struct netbuf *head,
            struct netbuf *tail);
 
 err_t             netbuf_data     (struct netbuf *buf,
-           void **dataptr, u16_t *len);
+                                   void **dataptr, u16_t *len);
 s8_t              netbuf_next     (struct netbuf *buf);
 void              netbuf_first    (struct netbuf *buf);
 
@@ -75,8 +85,12 @@ void              netbuf_first    (struct netbuf *buf);
 #define netbuf_fromport(buf)         ((buf)->port)
 #if LWIP_NETBUF_RECVINFO
 #define netbuf_destaddr(buf)         ((buf)->toaddr)
-#define netbuf_destport(buf)         ((buf)->toport)
+#define netbuf_destport(buf)         (((buf)->flags & NETBUF_FLAG_DESTADDR) ? (buf)->toport_chksum : 0)
 #endif /* LWIP_NETBUF_RECVINFO */
+#if LWIP_CHECKSUM_ON_COPY
+#define netbuf_set_chksum(buf, chksum) do { (buf)->flags = NETBUF_FLAG_CHKSUM; \
+                                            (buf)->toport_chksum = chksum; } while(0)
+#endif /* LWIP_CHECKSUM_ON_COPY */
 
 #ifdef __cplusplus
 }