diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 5b15d9d..e1f8941 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -750,7 +750,7 @@
 {
 	struct acm *acm = tty->driver_data;
 	if (!ACM_READY(acm))
-		return -EINVAL;
+		return 0;
 	/*
 	 * This is inaccurate (overcounts), but it works.
 	 */