diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
index 75658717961f4ac6603890ab785d444cfe864c3d..faac2f4e0f3ad358699a55123ebe18b38e8f65f5 100644
--- a/drivers/media/v4l2-core/v4l2-ioctl.c
+++ b/drivers/media/v4l2-core/v4l2-ioctl.c
@@ -1017,6 +1017,12 @@ static int v4l_querycap(const struct v4l2_ioctl_ops *ops,
 	ret = ops->vidioc_querycap(file, fh, cap);
 
 	cap->capabilities |= V4L2_CAP_EXT_PIX_FORMAT;
+	/*
+	 * Drivers MUST fill in device_caps, so check for this and
+	 * warn if it was forgotten.
+	 */
+	WARN_ON(!(cap->capabilities & V4L2_CAP_DEVICE_CAPS) ||
+		!cap->device_caps);
 	cap->device_caps |= V4L2_CAP_EXT_PIX_FORMAT;
 
 	return ret;