diff --git a/include/freetype/internal/t1types.h b/include/freetype/internal/t1types.h
index a4ea66b01..5a105c587 100644
--- a/include/freetype/internal/t1types.h
+++ b/include/freetype/internal/t1types.h
@@ -172,8 +172,8 @@ FT_BEGIN_HEADER
   {
     FT_Bool        IsCIDFont;
     FT_BBox        FontBBox;
-    FT_Fixed       Ascender;
-    FT_Fixed       Descender;
+    FT_Fixed       Ascender;     /* optional, mind the zero */
+    FT_Fixed       Descender;    /* optional, mind the zero */
     AFM_TrackKern  TrackKerns;   /* free if non-NULL */
     FT_UInt        NumTrackKern;
     AFM_KernPair   KernPairs;    /* free if non-NULL */