diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
index f051b151580d7de14647213f6c4497a75a4eff57..d10668f146997d07c53630b722d15fad2054ed98 100644
--- a/drivers/acpi/video.c
+++ b/drivers/acpi/video.c
@@ -812,7 +812,7 @@ acpi_video_device_write_brightness(struct file *file,
 
 	ACPI_FUNCTION_TRACE("acpi_video_device_write_brightness");
 
-	if (!dev || count + 1 > sizeof str)
+	if (!dev || !dev->brightness || count + 1 > sizeof str)
 		return_VALUE(-EINVAL);
 
 	if (copy_from_user(str, buffer, count))