diff --git a/drivers/tty/serial/serial_mctrl_gpio.h b/drivers/tty/serial/serial_mctrl_gpio.h
index 3c4ac9ae41f92914d4cce0e398b06e94e9d02a93..9716db283290697165002860430ab77bdb2ace00 100644
--- a/drivers/tty/serial/serial_mctrl_gpio.h
+++ b/drivers/tty/serial/serial_mctrl_gpio.h
@@ -133,11 +133,11 @@ void mctrl_gpio_free(struct device *dev, struct mctrl_gpios *gpios)
 {
 }
 
-void mctrl_gpio_enable_ms(struct mctrl_gpios *gpios)
+static inline void mctrl_gpio_enable_ms(struct mctrl_gpios *gpios)
 {
 }
 
-void mctrl_gpio_disable_ms(struct mctrl_gpios *gpios)
+static inline void mctrl_gpio_disable_ms(struct mctrl_gpios *gpios)
 {
 }