diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 23df1549eb0d..768b920e358f 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -408,11 +408,16 @@ static int acm_submit_read_urbs(struct acm *acm, gfp_t mem_flags)
 
 static void acm_process_read_urb(struct acm *acm, struct urb *urb)
 {
+	unsigned long flags;
+
 	if (!urb->actual_length)
 		return;
 
+	spin_lock_irqsave(&acm->read_lock, flags);
 	tty_insert_flip_string(&acm->port, urb->transfer_buffer,
 			urb->actual_length);
+	spin_unlock_irqrestore(&acm->read_lock, flags);
+
 	tty_flip_buffer_push(&acm->port);
 }