diff --git a/src/drivers/boards/px4fmu-v4pro/board_config.h b/src/drivers/boards/px4fmu-v4pro/board_config.h
index bb73eb487b..fd279db638 100644
--- a/src/drivers/boards/px4fmu-v4pro/board_config.h
+++ b/src/drivers/boards/px4fmu-v4pro/board_config.h
@@ -292,6 +292,9 @@
 #define PWMIN_TIMER_CHANNEL 2
 #define GPIO_PWM_IN			GPIO_TIM4_CH2IN_2
 
+/* N.B. By the virtue of not being named GPIO_BTN_SAFETY, this pin is
+ * initialized but not used (compiled for) in the FMU module
+ */
 #define GPIO_BTN_SAFETY_FMU		(GPIO_INPUT|GPIO_FLOAT|GPIO_PORTC|GPIO_PIN4)
 #define GPIO_SBUS_INV			(GPIO_OUTPUT|GPIO_PUSHPULL|GPIO_SPEED_2MHz|GPIO_OUTPUT_SET|GPIO_PORTC|GPIO_PIN13)
 #define BOARD_INVERT_RC_INPUT(_invert_true, _na)  px4_arch_gpiowrite(GPIO_SBUS_INV, _invert_true)