diff --git a/drivers/tty/serial/serial_port.c b/drivers/tty/serial/serial_port.c
index 85285c56fabf..2fc48cd63f6c 100644
--- a/drivers/tty/serial/serial_port.c
+++ b/drivers/tty/serial/serial_port.c
@@ -229,14 +229,15 @@ static int __uart_read_properties(struct uart_port *port, bool use_defaults)
 			break;
 		default:
 			port->iotype = UPIO_UNKNOWN;
-			if (!use_defaults) {
-				dev_err(dev, "Unsupported reg-io-width (%u)\n", value);
-				return -EINVAL;
-			}
 			break;
 		}
 	}
 
+	if (!use_defaults && port->iotype == UPIO_UNKNOWN) {
+		dev_err(dev, "Unsupported reg-io-width (%u)\n", value);
+		return -EINVAL;
+	}
+
 	/* Read the address mapping base offset (default: no offset) */
 	ret = device_property_read_u32(dev, "reg-offset", &value);
 	if (ret)