diff --git a/drivers/ata/pata_radisys.c b/drivers/ata/pata_radisys.c
index 4401b33..4fd25e7 100644
--- a/drivers/ata/pata_radisys.c
+++ b/drivers/ata/pata_radisys.c
@@ -139,9 +139,9 @@
 		pci_read_config_byte(dev, 0x4A, &udma_mode);
 
 		if (adev->xfer_mode == XFER_UDMA_2)
-			udma_mode &= ~ (1 << adev->devno);
+			udma_mode &= ~(2 << (adev->devno * 4));
 		else /* UDMA 4 */
-			udma_mode |= (1 << adev->devno);
+			udma_mode |= (2 << (adev->devno * 4));
 
 		pci_write_config_byte(dev, 0x4A, udma_mode);