diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index 4849b865b9085142aa5cf7e4ecf4f8297aca95ab..06142c1469cc4d95b84fed191544ffa110f82192 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -345,7 +345,8 @@ struct vb2_buffer {
  *			waiting for a new buffer to arrive.
  * @buf_out_validate:	called when the output buffer is prepared or queued
  *			to a request; drivers can use this to validate
- *			userspace-provided information; optional.
+ *			userspace-provided information; this is required only
+ *			for OUTPUT queues.
  * @buf_init:		called once after allocating a buffer (in MMAP case)
  *			or after acquiring a new USERPTR buffer; drivers may
  *			perform additional buffer-related initialization;