diff --git a/src/hb-ot-shape.cc b/src/hb-ot-shape.cc
index 36155dfca..a729c3f81 100644
--- a/src/hb-ot-shape.cc
+++ b/src/hb-ot-shape.cc
@@ -277,10 +277,10 @@ hb_ot_shape_execute_internal (hb_ot_shape_context_t *c)
   /* Save the original direction, we use it later. */
   c->original_direction = c->buffer->props.direction;
 
-  hb_ot_shape_setup_masks (c);
-
   hb_form_clusters (c);
 
+  hb_ot_shape_setup_masks (c);
+
   /* SUBSTITUTE */
   {
     /* Mirroring needs to see the original direction */