diff --git a/drivers/mmc/mmc_block.c b/drivers/mmc/mmc_block.c
index b5b4a7b..d4eee99 100644
--- a/drivers/mmc/mmc_block.c
+++ b/drivers/mmc/mmc_block.c
@@ -383,7 +383,10 @@
 	struct mmc_blk_data *md;
 	int err;
 
-	if (card->csd.cmdclass & ~0x1ff)
+	/*
+	 * Check that the card supports the command class(es) we need.
+	 */
+	if (!(card->csd.cmdclass & CCC_BLOCK_READ))
 		return -ENODEV;
 
 	if (card->csd.read_blkbits < 9) {