diff --git a/drivers/net/mmnif.c b/drivers/net/mmnif.c
index b76a3192..de3d32a7 100644
--- a/drivers/net/mmnif.c
+++ b/drivers/net/mmnif.c
@@ -563,7 +563,7 @@ err_t mmnif_tx(struct netif* netif, struct pbuf* p)
         uint8_t		build_buff = TRUE;
         uint32_t	dest_ip = mmnif_get_destination(netif,p);
 
-        mm_rx_buffer_t* rb = (mm_rx_buffer_t*)((char*)mpb_start_address + ( dest -1 ) * mpb_size);
+        mm_rx_buffer_t* rb = (mm_rx_buffer_t*)((char*)mpb_start_address + ( dest_ip -1 ) * mpb_size);
 
 #ifdef WIN32
         ReadProcessMemory(hProc, (char*)mpb_start_address + ( dest_ip -1 ) * mpb_size, (char*)mpb_start_address + ( dest_ip -1 ) * mpb_size,mpb_size,NULL);