diff --git a/src/hb-ot-layout.cc b/src/hb-ot-layout.cc
index a7607f626..108144388 100644
--- a/src/hb-ot-layout.cc
+++ b/src/hb-ot-layout.cc
@@ -952,6 +952,32 @@ hb_ot_layout_lookup_substitute_closure (hb_face_t    *face,
   l.closure (&c, lookup_index);
 }
 
+/**
+ * hb_ot_layout_lookups_substitute_closure:
+ *
+ * Compute the transitive closure of glyphs needed for all of the
+ * provided lookups.
+ *
+ * Since: 1.8.1
+ **/
+void
+hb_ot_layout_lookups_substitute_closure (hb_face_t      *face,
+                                         const hb_set_t *lookups,
+                                         hb_set_t       *glyphs)
+{
+  hb_auto_t<hb_map_t> done_lookups;
+  OT::hb_closure_context_t c (face, glyphs, &done_lookups);
+  const OT::GSUB& gsub = _get_gsub (face);
+
+  unsigned int glyphs_length;
+  do
+  {
+    glyphs_length = glyphs->get_population ();
+    for (hb_codepoint_t lookup_index = HB_SET_VALUE_INVALID; hb_set_next (lookups, &lookup_index);)
+      gsub.get_lookup (lookup_index).closure (&c, lookup_index);
+  } while (glyphs_length != glyphs->get_population ());
+}
+
 /*
  * OT::GPOS
  */
diff --git a/src/hb-ot-layout.h b/src/hb-ot-layout.h
index d82dc0226..027879622 100644
--- a/src/hb-ot-layout.h
+++ b/src/hb-ot-layout.h
@@ -277,6 +277,12 @@ hb_ot_layout_lookup_substitute_closure (hb_face_t    *face,
 				        hb_set_t     *glyphs
 					/*TODO , hb_bool_t  inclusive */);
 
+HB_EXTERN void
+hb_ot_layout_lookups_substitute_closure (hb_face_t      *face,
+                                         const hb_set_t *lookups,
+                                         hb_set_t       *glyphs);
+
+
 #ifdef HB_NOT_IMPLEMENTED
 /* Note: You better have GDEF when using this API, or marks won't do much. */
 HB_EXTERN hb_bool_t
diff --git a/src/hb-ot-shape.cc b/src/hb-ot-shape.cc
index c20b110e2..36e0bf9c3 100644
--- a/src/hb-ot-shape.cc
+++ b/src/hb-ot-shape.cc
@@ -957,15 +957,7 @@ hb_ot_shape_glyphs_closure (hb_font_t          *font,
 
   hb_set_t *lookups = hb_set_create ();
   hb_ot_shape_plan_collect_lookups (shape_plan, HB_OT_TAG_GSUB, lookups);
-
-  /* And find transitive closure. */
-  hb_set_t *copy = hb_set_create ();
-  do {
-    copy->set (glyphs);
-    for (hb_codepoint_t lookup_index = HB_SET_VALUE_INVALID; hb_set_next (lookups, &lookup_index);)
-      hb_ot_layout_lookup_substitute_closure (font->face, lookup_index, glyphs);
-  } while (!copy->is_equal (glyphs));
-  hb_set_destroy (copy);
+  hb_ot_layout_lookups_substitute_closure (font->face, lookups, glyphs);
 
   hb_set_destroy (lookups);