diff --git a/drivers/mfd/sm501.c b/drivers/mfd/sm501.c
index c707c8ebc1a2..b0b4458ae90b 100644
--- a/drivers/mfd/sm501.c
+++ b/drivers/mfd/sm501.c
@@ -319,7 +319,7 @@ int sm501_unit_power(struct device *dev, unsigned int unit, unsigned int to)
 
 	mode &= 3;		/* get current power mode */
 
-	if (unit > ARRAY_SIZE(sm->unit_power)) {
+	if (unit >= ARRAY_SIZE(sm->unit_power)) {
 		dev_err(dev, "%s: bad unit %d\n", __FUNCTION__, unit);
 		goto already;
 	}