diff --git a/src/hb-ot-shape-normalize.cc b/src/hb-ot-shape-normalize.cc
index b9834ca10872c9638b79bc0ee0d85248490b3b5a..0bcf7f58a7427774cd784e91c2f20dbeefdac6f6 100644
--- a/src/hb-ot-shape-normalize.cc
+++ b/src/hb-ot-shape-normalize.cc
@@ -269,6 +269,7 @@ _hb_ot_shape_normalize (hb_font_t *font, hb_buffer_t *buffer,
     {
       /* Composes. Modify starter and carry on. */
       buffer->out_info[starter].codepoint = composed;
+      /* XXX update cluster */
       set_unicode_props (&buffer->out_info[starter], buffer->unicode);
 
       buffer->skip_glyph ();