diff --git a/libavutil/frame.h b/libavutil/frame.h
index 6b9ac6ae2c..2fab79e58b 100644
--- a/libavutil/frame.h
+++ b/libavutil/frame.h
@@ -124,6 +124,13 @@ enum AVActiveFormatDescription {
     AV_AFD_SP_4_3       = 15,
 };
 
+
+/**
+ * Structure to hold side data for an AVFrame.
+ *
+ * sizeof(AVFrameSideData) is not a part of the public ABI, so new fields may be added
+ * to the end with a minor bump.
+ */
 typedef struct AVFrameSideData {
     enum AVFrameSideDataType type;
     uint8_t *data;