diff --git a/drivers/net/designware.c b/drivers/net/designware.c
index 4fa26ab..01abcc2 100644
--- a/drivers/net/designware.c
+++ b/drivers/net/designware.c
@@ -389,15 +389,17 @@
 
 #if defined(CONFIG_DW_ALTDESCRIPTOR)
 	desc_p->txrx_status |= DESC_TXSTS_TXFIRST | DESC_TXSTS_TXLAST;
-	desc_p->dmamac_cntl |= (length << DESC_TXCTRL_SIZE1SHFT) &
-			       DESC_TXCTRL_SIZE1MASK;
+	desc_p->dmamac_cntl = (desc_p->dmamac_cntl & ~DESC_TXCTRL_SIZE1MASK) |
+			      ((length << DESC_TXCTRL_SIZE1SHFT) &
+			      DESC_TXCTRL_SIZE1MASK);
 
 	desc_p->txrx_status &= ~(DESC_TXSTS_MSK);
 	desc_p->txrx_status |= DESC_TXSTS_OWNBYDMA;
 #else
-	desc_p->dmamac_cntl |= ((length << DESC_TXCTRL_SIZE1SHFT) &
-			       DESC_TXCTRL_SIZE1MASK) | DESC_TXCTRL_TXLAST |
-			       DESC_TXCTRL_TXFIRST;
+	desc_p->dmamac_cntl = (desc_p->dmamac_cntl & ~DESC_TXCTRL_SIZE1MASK) |
+			      ((length << DESC_TXCTRL_SIZE1SHFT) &
+			      DESC_TXCTRL_SIZE1MASK) | DESC_TXCTRL_TXLAST |
+			      DESC_TXCTRL_TXFIRST;
 
 	desc_p->txrx_status = DESC_TXSTS_OWNBYDMA;
 #endif