diff --git a/drivers/net/rtl8139.c b/drivers/net/rtl8139.c
index df5d7ce6..42e6f9e9 100644
--- a/drivers/net/rtl8139.c
+++ b/drivers/net/rtl8139.c
@@ -36,6 +36,9 @@
 #include <netif/etharp.h>
 #include <net/rtl8139.h>
 
+#define RX_BUF_LEN 	8192
+#define TX_BUF_LEN	4096
+
 board_t board_tbl[] = 
 {
 	{"RealTek", "RealTek RTL8139", 0x10ec, 0x8139},
@@ -153,11 +156,11 @@ static void rtl_rx_inthandler(struct netif* netif)
 	cmd = inportb(rtl8139if->iobase + CR);
 	while(!(cmd & CR_BUFE)) {
 		header = *((uint16_t*) (rtl8139if->rx_buffer+rtl8139if->rx_pos));
-		rtl8139if->rx_pos = (rtl8139if->rx_pos + 2) % (8192+16);
+		rtl8139if->rx_pos = (rtl8139if->rx_pos + 2) % RX_BUF_LEN;
 
 		if (header & ISR_ROK) {
 			length = *((uint16_t*) (rtl8139if->rx_buffer+rtl8139if->rx_pos)) - 4; // copy packet (but not the CRC)
-			rtl8139if->rx_pos = (rtl8139if->rx_pos + 2) % (8192+16);
+			rtl8139if->rx_pos = (rtl8139if->rx_pos + 2) % RX_BUF_LEN;
 #if ETH_PAD_SIZE
 			length += ETH_PAD_SIZE; /* allow room for Ethernet padding */
 #endif
@@ -170,7 +173,7 @@ static void rtl_rx_inthandler(struct netif* netif)
 				for (q=p; q!=NULL; q=q->next) {
 					for(i=0; i<q->len; i++) {
 						((uint8_t*) q->payload)[i] = rtl8139if->rx_buffer[rtl8139if->rx_pos];
-						rtl8139if->rx_pos = (rtl8139if->rx_pos + 1) % (8192+16);
+						rtl8139if->rx_pos = (rtl8139if->rx_pos + 1) % RX_BUF_LEN;
 					}	
  				}
 #if ETH_PAD_SIZE
@@ -180,16 +183,16 @@ static void rtl_rx_inthandler(struct netif* netif)
 				LINK_STATS_INC(link.recv);
 			} else {
 				LWIP_DEBUGF(NETIF_DEBUG, ("rtl8139if_rx_inthandler: not enough memory!\n"));
-				rtl8139if->rx_pos += (rtl8139if->rx_pos + length) % (8192+16);
+				rtl8139if->rx_pos += (rtl8139if->rx_pos + length) % RX_BUF_LEN;
 				LINK_STATS_INC(link.memerr);
 				LINK_STATS_INC(link.drop);
 			}
 
 			// packets are dword aligned
-			rtl8139if->rx_pos = ((rtl8139if->rx_pos + 4 + 3) & ~0x3) % (8192+16);
+			rtl8139if->rx_pos = ((rtl8139if->rx_pos + 4 + 3) & ~0x3) % RX_BUF_LEN;
 			outportw(rtl8139if->iobase + CAPR, rtl8139if->rx_pos - 0x10);
 		} else {
-			LWIP_DEBUGF(NETIF_DEBUG, ("rtl8139if_rx_inthandler: invalid header!\n"));
+			LWIP_DEBUGF(NETIF_DEBUG, ("rtl8139if_rx_inthandler: invalid header 0x%x, rx_pos %d\n", (uint32_t) header, rtl8139if->rx_pos));
 			LINK_STATS_INC(link.memerr);
 			LINK_STATS_INC(link.drop);
 			break;
@@ -287,26 +290,26 @@ err_t rtl8139if_init(struct netif* netif)
 	memset(rtl8139if, 0, sizeof(rtl1839if_t));
 
 	/* allocate the receive buffer */
-	rtl8139if->rx_buffer = mem_allocation(8192+16, MAP_KERNEL_SPACE|MAP_NO_CACHE);
+	rtl8139if->rx_buffer = mem_allocation(RX_BUF_LEN/*+16*/, MAP_KERNEL_SPACE|MAP_NO_CACHE);
 	if (!(rtl8139if->rx_buffer)) {
 		LWIP_DEBUGF(NETIF_DEBUG, ("rtl8139if_init: out of memory\n"));
 		kfree(rtl8139if, sizeof(rtl1839if_t));
 		return ERR_MEM;
 	}
-	memset(rtl8139if->rx_buffer, 0, 8192+16);
+	memset(rtl8139if->rx_buffer, 0x00, RX_BUF_LEN);
 
 	/* allocate the send buffers */
-	rtl8139if->tx_buffer[0] = mem_allocation(4*4096, MAP_KERNEL_SPACE|MAP_NO_CACHE);
+	rtl8139if->tx_buffer[0] = mem_allocation(4*TX_BUF_LEN, MAP_KERNEL_SPACE|MAP_NO_CACHE);
 	if (!(rtl8139if->tx_buffer[0])) {
 		LWIP_DEBUGF(NETIF_DEBUG, ("rtl8139if_init: out of memory\n"));
-		kfree(rtl8139if->rx_buffer, 8192+16);
+		kfree(rtl8139if->rx_buffer, RX_BUF_LEN);
 		kfree(rtl8139if, sizeof(rtl1839if_t));
 		return ERR_MEM;
 	}
-	memset(rtl8139if->tx_buffer[0], 0, 4*4096);
-	rtl8139if->tx_buffer[1] = rtl8139if->tx_buffer[0] + 4096;
-	rtl8139if->tx_buffer[2] = rtl8139if->tx_buffer[1] + 4096;
-	rtl8139if->tx_buffer[3] = rtl8139if->tx_buffer[2] + 4096;
+	memset(rtl8139if->tx_buffer[0], 0x00, 4*TX_BUF_LEN);
+	rtl8139if->tx_buffer[1] = rtl8139if->tx_buffer[0] + TX_BUF_LEN;
+	rtl8139if->tx_buffer[2] = rtl8139if->tx_buffer[1] + TX_BUF_LEN;
+	rtl8139if->tx_buffer[3] = rtl8139if->tx_buffer[2] + TX_BUF_LEN;
 
 	netif->state = rtl8139if;
 	mynetif = netif;