diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index dc362fa01ca46f44680018fde3b5372f03d7f57b..f6408ca82062f9375228158be9e9b23aa9cd0846 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -3455,7 +3455,8 @@ static void ata_dev_xfermask(struct ata_device *dev)
 			       "device is on DMA blacklist, disabling DMA\n");
 	}
 
-	if ((host->flags & ATA_HOST_SIMPLEX) && host->simplex_claimed != ap) {
+	if ((host->flags & ATA_HOST_SIMPLEX) &&
+            host->simplex_claimed && host->simplex_claimed != ap) {
 		xfer_mask &= ~(ATA_MASK_MWDMA | ATA_MASK_UDMA);
 		ata_dev_printk(dev, KERN_WARNING, "simplex DMA is claimed by "
 			       "other device, disabling DMA\n");