diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
index cf75beb..31d2768 100644
--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -375,6 +375,22 @@
 	return count;
 }
 
+static void serial_wait_until_sent(struct tty_struct *tty, int timeout)
+{
+	struct usb_serial_port *port = tty->driver_data;
+	struct usb_serial *serial = port->serial;
+
+	dev_dbg(tty->dev, "%s\n", __func__);
+
+	if (!port->serial->type->wait_until_sent)
+		return;
+
+	mutex_lock(&serial->disc_mutex);
+	if (!serial->disconnected)
+		port->serial->type->wait_until_sent(tty, timeout);
+	mutex_unlock(&serial->disc_mutex);
+}
+
 static void serial_throttle(struct tty_struct *tty)
 {
 	struct usb_serial_port *port = tty->driver_data;
@@ -1191,6 +1207,7 @@
 	.unthrottle =		serial_unthrottle,
 	.break_ctl =		serial_break,
 	.chars_in_buffer =	serial_chars_in_buffer,
+	.wait_until_sent =	serial_wait_until_sent,
 	.tiocmget =		serial_tiocmget,
 	.tiocmset =		serial_tiocmset,
 	.get_icount =		serial_get_icount,