diff --git a/src/OT/Layout/GPOS/SinglePosFormat1.hh b/src/OT/Layout/GPOS/SinglePosFormat1.hh
index 2ae692831..1de8a36c4 100644
--- a/src/OT/Layout/GPOS/SinglePosFormat1.hh
+++ b/src/OT/Layout/GPOS/SinglePosFormat1.hh
@@ -104,9 +104,11 @@ struct SinglePosFormat1
     const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
     const hb_map_t &glyph_map = *c->plan->glyph_map;
 
+    hb_set_t intersection;
+    (this+coverage).intersected_coverage_glyphs (&glyphset, &intersection);
+
     auto it =
-    + hb_iter (glyphset)
-    | hb_filter (this+coverage)
+    + hb_iter (intersection)
     | hb_map_retains_sorting (glyph_map)
     | hb_zip (hb_repeat (values.as_array (valueFormat.get_len ())))
     ;
diff --git a/src/OT/Layout/GSUB/SingleSubstFormat1.hh b/src/OT/Layout/GSUB/SingleSubstFormat1.hh
index cef19cf91..b57be0ad1 100644
--- a/src/OT/Layout/GSUB/SingleSubstFormat1.hh
+++ b/src/OT/Layout/GSUB/SingleSubstFormat1.hh
@@ -135,38 +135,8 @@ struct SingleSubstFormat1_3
     hb_codepoint_t d = deltaGlyphID;
     hb_codepoint_t mask = get_mask ();
 
-    hb_sorted_vector_t<hb_codepoint_t> intersection;
-    if (1)
-    {
-      /* Walk the coverage and set together, to bail out when the
-       * coverage iterator runs over the end of glyphset. Otherwise,
-       * the coverage may cover many glyphs and we spend a lot of
-       * time here.  Other subtables don't have this problem because
-       * they zip coverage iterator with some array... */
-      auto c_iter = hb_iter (this+coverage);
-      auto s_iter = hb_iter (glyphset);
-      while (c_iter && s_iter)
-      {
-	hb_codepoint_t cv = *c_iter;
-	hb_codepoint_t sv = *s_iter;
-	if (cv == sv)
-	{
-	  intersection.push (cv);
-	  c_iter++;
-	  s_iter++;
-	}
-	else if (cv < sv)
-	  c_iter++;
-	else
-	  s_iter++;
-      }
-    }
-    else
-    {
-      + hb_iter (this+coverage)
-      | hb_filter (glyphset)
-      | hb_sink (intersection);
-    }
+    hb_set_t intersection;
+    (this+coverage).intersected_coverage_glyphs (&glyphset, &intersection);
 
     auto it =
     + hb_iter (intersection)