diff --git a/drivers/tty/serial/max310x.c b/drivers/tty/serial/max310x.c
index eb040d8292a8..0a04c053654f 100644
--- a/drivers/tty/serial/max310x.c
+++ b/drivers/tty/serial/max310x.c
@@ -1197,8 +1197,7 @@ static int max310x_probe(struct device *dev, struct max310x_devtype *devtype,
 		return PTR_ERR(regmap);
 
 	/* Alloc port structure */
-	s = devm_kzalloc(dev, sizeof(*s) +
-			 sizeof(struct max310x_one) * devtype->nr, GFP_KERNEL);
+	s = devm_kzalloc(dev, struct_size(s, p, devtype->nr), GFP_KERNEL);
 	if (!s) {
 		dev_err(dev, "Error allocating port structure\n");
 		return -ENOMEM;