diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 467a4f1..c356c0a 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -447,7 +447,7 @@
 		for (i=0; i< MAX_MTD_DEVICES; i++)
 			if (mtd_table[i] == mtd)
 				ret = mtd_table[i];
-	} else if (num < MAX_MTD_DEVICES) {
+	} else if (num >= 0 && num < MAX_MTD_DEVICES) {
 		ret = mtd_table[num];
 		if (mtd && mtd != ret)
 			ret = NULL;
diff --git a/drivers/mtd/nand/fsl_upm.c b/drivers/mtd/nand/fsl_upm.c
index d120cd8..071a60c 100644
--- a/drivers/mtd/nand/fsl_upm.c
+++ b/drivers/mtd/nand/fsl_upm.c
@@ -112,7 +112,7 @@
 
 	if (mchip_nr == -1) {
 		chip->cmd_ctrl(mtd, NAND_CMD_NONE, 0 | NAND_CTRL_CHANGE);
-	} else if (mchip_nr >= 0) {
+	} else if (mchip_nr >= 0 && mchip_nr < NAND_MAX_CHIPS) {
 		fun->mchip_number = mchip_nr;
 		chip->IO_ADDR_R = fun->io_base + fun->mchip_offsets[mchip_nr];
 		chip->IO_ADDR_W = chip->IO_ADDR_R;