diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c
index 843798e630844..90953e679e386 100644
--- a/drivers/tty/serial/msm_serial.c
+++ b/drivers/tty/serial/msm_serial.c
@@ -1120,6 +1120,7 @@ msm_find_best_baud(struct uart_port *port, unsigned int baud,
 
 static int msm_set_baud_rate(struct uart_port *port, unsigned int baud,
 			     unsigned long *saved_flags)
+	__must_hold(&port->lock)
 {
 	unsigned int rxstale, watermark, mask;
 	struct msm_port *msm_port = to_msm_port(port);