diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index f298a18b1f69..6b1ee11295d5 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -126,6 +126,8 @@ config GPIO_RASPBERRYPI_EXP
 	tristate "Raspberry Pi 3 GPIO Expander"
 	default RASPBERRYPI_FIRMWARE
 	depends on OF_GPIO
+	# Make sure not 'y' when RASPBERRYPI_FIRMWARE is 'm'. This can only
+	# happen when COMPILE_TEST=y, hence the added !RASPBERRYPI_FIRMWARE.
 	depends on (ARCH_BCM2835 && RASPBERRYPI_FIRMWARE) || (COMPILE_TEST && !RASPBERRYPI_FIRMWARE)
 	help
 	  Turn on GPIO support for the expander on Raspberry Pi 3 boards, using