diff --git a/drivers/ata/pata_efar.c b/drivers/ata/pata_efar.c
index 540c36426303..f37d98700dfd 100644
--- a/drivers/ata/pata_efar.c
+++ b/drivers/ata/pata_efar.c
@@ -201,7 +201,7 @@ static void efar_set_dmamode (struct ata_port *ap, struct ata_device *adev)
 			master_data &= 0xFF4F;  /* Mask out IORDY|TIME1|DMAONLY */
 			master_data |= control << 4;
 			pci_read_config_byte(dev, 0x44, &slave_data);
-			slave_data &= (0x0F + 0xE1 * ap->port_no);
+			slave_data &= ap->port_no ? 0x0F : 0xF0;
 			/* Load the matching timing */
 			slave_data |= ((timings[pio][0] << 2) | timings[pio][1]) << (ap->port_no ? 4 : 0);
 			pci_write_config_byte(dev, 0x44, slave_data);