diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 2b9b511..b774f9d 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -1716,9 +1716,12 @@ static ssize_t latency_timer_store(struct device *dev,
 {
 	struct usb_serial_port *port = to_usb_serial_port(dev);
 	struct ftdi_private *priv = usb_get_serial_port_data(port);
-	int v = simple_strtoul(valbuf, NULL, 10);
+	u8 v;
 	int rv;
 
+	if (kstrtou8(valbuf, 10, &v))
+		return -EINVAL;
+
 	priv->latency = v;
 	rv = write_latency_timer(port);
 	if (rv < 0)