diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index fe4aeb2c8b..f4605bec81 100644
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -897,7 +897,8 @@ typedef struct AVCodecContext {
     /**
      * called at the beginning of each frame to get a buffer for it.
      * if pic.reference is set then the frame will be read later by lavc
-     * width and height should be rounded up to the next multiple of 16
+     * avcodec_align_dimensions() should be used to find the required width and
+     * height, as they normally need to be rounded up to the next multiple of 16
      * - encoding: unused
      * - decoding: set by lavc, user can override
      */