diff --git a/include/freetype/tttables.h b/include/freetype/tttables.h
index 111f21802..2cf0ff1bc 100644
--- a/include/freetype/tttables.h
+++ b/include/freetype/tttables.h
@@ -838,8 +838,9 @@ FT_BEGIN_HEADER
    *     The target charmap.
    *
    * @return:
-   *   The format of `charmap`.  If `charmap` doesn't belong to an SFNT face,
-   *   return -1.
+   *   The format of `charmap`.  If `charmap` doesn't belong to an SFNT face
+   *   (including the synthetic Unicode charmap sometimes created by
+   *   FreeType), return -1.
    */
   FT_EXPORT( FT_Long )
   FT_Get_CMap_Format( FT_CharMap  charmap );