diff --git a/drivers/net/ucc_geth.c b/drivers/net/ucc_geth.c
index 9a38dfe..5900847 100644
--- a/drivers/net/ucc_geth.c
+++ b/drivers/net/ucc_geth.c
@@ -1533,10 +1698,17 @@ static void adjust_link(struct net_device *dev)
 		 * If not, we operate in half-duplex mode. */
 		if (phydev->duplex != ugeth->oldduplex) {
 			new_state = 1;
-			if (!(phydev->duplex))
-				tempval &= ~(MACCFG2_FDX);
-			else
-				tempval |= MACCFG2_FDX;
+			/* Can only use half duplex for these two modes!! */
+			if ((ugeth->phy_interface == PHY_INTERFACE_MODE_MII) ||
+			  (ugeth->phy_interface == PHY_INTERFACE_MODE_RMII)) {	
+				if (!(phydev->duplex))
+					tempval &= ~(MACCFG2_FDX);
+				else
+					tempval |= MACCFG2_FDX;
+			} else {
+				/* Always set for other modes */
+				tempval |= MACCFG2_FDX; 
+			}
 			ugeth->oldduplex = phydev->duplex;
 		}