diff --git a/libraries/net/eth/lwip-eth/arch/lpc17_emac.c b/libraries/net/eth/lwip-eth/arch/lpc17_emac.c
index 243f9930a0..729840f636 100644
--- a/libraries/net/eth/lwip-eth/arch/lpc17_emac.c
+++ b/libraries/net/eth/lwip-eth/arch/lpc17_emac.c
@@ -88,6 +88,10 @@
  */
 #define TXINTGROUP (EMAC_INT_TX_UNDERRUN | EMAC_INT_TX_ERR | EMAC_INT_TX_DONE)
 
+/** \brief  Signal used for ethernet ISR to signal packet_rx() thread.
+ */
+#define RX_SIGNAL  1
+
 #else
 #define RXINTGROUP 0
 #define TXINTGROUP 0
@@ -123,7 +127,7 @@ struct lpc_enetdata {
 	struct pbuf *txb[LPC_NUM_BUFF_TXDESCS]; /**< TX pbuf pointer list, zero-copy mode */
 	u32_t lpc_last_tx_idx; /**< TX last descriptor index, zero-copy mode */
 #if NO_SYS == 0
-	sys_sem_t RxSem; /**< RX receive thread wakeup semaphore */
+	sys_thread_t RxThread; /**< RX receive thread data object pointer */
 	sys_sem_t TxCleanSem; /**< TX cleanup thread wakeup semaphore */
 	sys_mutex_t TXLockMutex; /**< TX critical section mutex */
 	sys_sem_t xTXDCountSem; /**< TX free buffer counting semaphore */
@@ -346,6 +350,7 @@ static struct pbuf *lpc_low_level_input(struct netif *netif)
 	struct lpc_enetdata *lpc_enetif = netif->state;
 	struct pbuf *p = NULL;
 	u32_t idx, length;
+	u16_t origLength;
 
 #ifdef LOCK_RX_THREAD
 #if NO_SYS == 0
@@ -428,6 +433,7 @@ static struct pbuf *lpc_low_level_input(struct netif *netif)
 
 			/* Zero-copy */
 			p = lpc_enetif->rxb[idx];
+			origLength = p->len;
 			p->len = (u16_t) length;
 
 			/* Free pbuf from descriptor */
@@ -440,6 +446,7 @@ static struct pbuf *lpc_low_level_input(struct netif *netif)
     			LINK_STATS_INC(link.drop);
 
     			/* Re-queue the pbuf for receive */
+    			p->len = origLength;
     			lpc_rxqueue_pbuf(lpc_enetif, p);
 
     			LWIP_DEBUGF(UDP_LPC_EMAC | LWIP_DBG_TRACE,
@@ -780,8 +787,8 @@ void ENET_IRQHandler(void)
 	ints = LPC_EMAC->IntStatus;
 
 	if (ints & RXINTGROUP) {
-        /* RX group interrupt(s): Give semaphore to wakeup RX receive task.*/
-        sys_sem_signal(&lpc_enetdata.RxSem);
+        /* RX group interrupt(s): Give signal to wakeup RX receive task.*/
+        osSignalSet(lpc_enetdata.RxThread->id, RX_SIGNAL);
     }
 
     if (ints & TXINTGROUP) {
@@ -807,7 +814,7 @@ static void packet_rx(void* pvParameters) {
 
     while (1) {
         /* Wait for receive task to wakeup */
-        sys_arch_sem_wait(&lpc_enetif->RxSem, 0);
+        osSignalWait(RX_SIGNAL, osWaitForever);
 
         /* Process packets until all empty */
         while (LPC_EMAC->RxConsumeIndex != LPC_EMAC->RxProduceIndex)
@@ -1093,9 +1100,8 @@ err_t lpc_enetif_init(struct netif *netif)
 	LWIP_ASSERT("TXLockMutex creation error", (err == ERR_OK));
 
 	/* Packet receive task */
-	err = sys_sem_new(&lpc_enetdata.RxSem, 0);
-	LWIP_ASSERT("RxSem creation error", (err == ERR_OK));
-	sys_thread_new("receive_thread", packet_rx, netif->state, DEFAULT_THREAD_STACKSIZE, RX_PRIORITY);
+	lpc_enetdata.RxThread = sys_thread_new("receive_thread", packet_rx, netif->state, DEFAULT_THREAD_STACKSIZE, RX_PRIORITY);
+	LWIP_ASSERT("RxThread creation error", (lpc_enetdata.RxThread));
 
 	/* Transmit cleanup task */
 	err = sys_sem_new(&lpc_enetdata.TxCleanSem, 0);
diff --git a/libraries/net/lwip/lwip/core/pbuf.c b/libraries/net/lwip/lwip/core/pbuf.c
index 818eb62035..cd37c79723 100644
--- a/libraries/net/lwip/lwip/core/pbuf.c
+++ b/libraries/net/lwip/lwip/core/pbuf.c
@@ -998,6 +998,8 @@ pbuf_coalesce(struct pbuf *p, pbuf_layer layer)
   }
   err = pbuf_copy(q, p);
   LWIP_ASSERT("pbuf_copy failed", err == ERR_OK);
+  /* next line references err variable even if LWIP_ASSERT is ignored. */
+  (void)err;
   pbuf_free(p);
   return q;
 }
diff --git a/libraries/net/lwip/lwip/lwipopts.h b/libraries/net/lwip/lwip/lwipopts.h
index 10846e2416..4d07680dbc 100644
--- a/libraries/net/lwip/lwip/lwipopts.h
+++ b/libraries/net/lwip/lwip/lwipopts.h
@@ -27,6 +27,8 @@
 #if NO_SYS == 0
 #include "cmsis_os.h"
 
+#define SYS_LIGHTWEIGHT_PROT        1
+
 #define LWIP_RAW                    0
 
 #define TCPIP_MBOX_SIZE             8
@@ -99,6 +101,7 @@
 #define MEMP_OVERFLOW_CHECK         1
 #define MEMP_SANITY_CHECK           1
 #else
+#define LWIP_NOASSERT               1
 #define LWIP_STATS                  0
 #endif