diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
index 69e072b59127..7309594e1c12 100644
--- a/drivers/tty/tty_port.c
+++ b/drivers/tty/tty_port.c
@@ -227,6 +227,8 @@ out:
  *
  *	Perform port level tty hangup flag and count changes. Drop the tty
  *	reference.
+ *
+ *	Caller holds tty lock.
  */
 
 void tty_port_hangup(struct tty_port *port)