diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index a693381ed3cc..b84ccec8fc7b 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -626,8 +626,6 @@ static void acm_tty_unregister(struct acm *acm)
 	kfree(acm);
 }
 
-static int acm_tty_chars_in_buffer(struct tty_struct *tty);
-
 static void acm_port_down(struct acm *acm)
 {
 	int i, nr = acm->rx_buflimit;