diff --git a/libraries/net/eth/lwip-eth/arch/lpc_emac_config.h b/libraries/net/eth/lwip-eth/arch/lpc_emac_config.h
index 048f08b8a9b..831b3d76d09 100644
--- a/libraries/net/eth/lwip-eth/arch/lpc_emac_config.h
+++ b/libraries/net/eth/lwip-eth/arch/lpc_emac_config.h
@@ -86,7 +86,7 @@ extern "C"
 /** \brief  Defines the number of descriptors used for TX. Must
  *          be a minimum value of 2.
  */
-#define LPC_NUM_BUFF_TXDESCS 3
+#define LPC_NUM_BUFF_TXDESCS (TCP_SND_QUEUELEN + 1)
 
 /** \brief  Set this define to 1 to enable bounce buffers for transmit pbufs
  *          that cannot be sent via the zero-copy method. Some chained pbufs
diff --git a/libraries/net/lwip/lwip/core/tcp_out.c b/libraries/net/lwip/lwip/core/tcp_out.c
index 86e0919531f..0cc48b1cdb7 100644
--- a/libraries/net/lwip/lwip/core/tcp_out.c
+++ b/libraries/net/lwip/lwip/core/tcp_out.c
@@ -646,6 +646,9 @@ tcp_write(struct tcp_pcb *pcb, const void *arg, u16_t len, u8_t apiflags)
     last_unsent->len += concat_p->tot_len;
 #if TCP_CHECKSUM_ON_COPY
     if (concat_chksummed) {
+      if (concat_chksum_swapped) {
+        concat_chksum = SWAP_BYTES_IN_WORD(concat_chksum);
+      }
       tcp_seg_add_chksum(concat_chksum, concat_chksummed, &last_unsent->chksum,
         &last_unsent->chksum_swapped);
       last_unsent->flags |= TF_SEG_DATA_CHECKSUMMED;