diff --git a/src/hb-shape-plan.cc b/src/hb-shape-plan.cc
index b44a9e2ab..ab7926247 100644
--- a/src/hb-shape-plan.cc
+++ b/src/hb-shape-plan.cc
@@ -396,6 +396,8 @@ retry:
   }
 
   /* Release our reference on face. */
+  /* XXX This is unsafe, since the face can be freed before us,
+   * and we will call hb_face_destroy() in our destroy()! */
   hb_face_destroy (face);
 
   return hb_shape_plan_reference (shape_plan);