diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
index 31d2768..60caf9cb 100644
--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -1333,6 +1333,8 @@
 	set_to_generic_if_null(device, close);
 	set_to_generic_if_null(device, write_room);
 	set_to_generic_if_null(device, chars_in_buffer);
+	if (device->tx_empty)
+		set_to_generic_if_null(device, wait_until_sent);
 	set_to_generic_if_null(device, read_bulk_callback);
 	set_to_generic_if_null(device, write_bulk_callback);
 	set_to_generic_if_null(device, process_read_urb);