diff --git a/src/hb-ot-layout-common.hh b/src/hb-ot-layout-common.hh
index 0ba7e3c06..a5d7804c7 100644
--- a/src/hb-ot-layout-common.hh
+++ b/src/hb-ot-layout-common.hh
@@ -88,10 +88,10 @@ static inline void ClassDef_serialize (hb_serialize_context_t *c,
 				       Iterator it);
 
 static void ClassDef_remap_and_serialize (hb_serialize_context_t *c,
-					  const hb_set_t &glyphset,
 					  const hb_map_t &gid_klass_map,
 					  hb_sorted_vector_t<HBGlyphID> &glyphs,
 					  const hb_set_t &klasses,
+                                          bool use_class_zero,
 					  hb_map_t *klass_map /*INOUT*/);
 
 struct hb_subset_layout_context_t :
@@ -1645,10 +1645,10 @@ Coverage_serialize (hb_serialize_context_t *c,
 { c->start_embed<Coverage> ()->serialize (c, it); }
 
 static void ClassDef_remap_and_serialize (hb_serialize_context_t *c,
-					  const hb_set_t &glyphset,
 					  const hb_map_t &gid_klass_map,
 					  hb_sorted_vector_t<HBGlyphID> &glyphs,
 					  const hb_set_t &klasses,
+                                          bool use_class_zero,
 					  hb_map_t *klass_map /*INOUT*/)
 {
   if (!klass_map)
@@ -1660,7 +1660,7 @@ static void ClassDef_remap_and_serialize (hb_serialize_context_t *c,
 
   /* any glyph not assigned a class value falls into Class zero (0),
    * if any glyph assigned to class 0, remapping must start with 0->0*/
-  if (glyphset.get_population () > gid_klass_map.get_population ())
+  if (!use_class_zero)
     klass_map->set (0, 0);
 
   unsigned idx = klass_map->has (0) ? 1 : 0;
@@ -1730,7 +1730,9 @@ struct ClassDefFormat1
   }
 
   bool subset (hb_subset_context_t *c,
-	       hb_map_t *klass_map = nullptr /*OUT*/) const
+	       hb_map_t *klass_map = nullptr /*OUT*/,
+               bool use_class_zero = true,
+               const Coverage* glyph_filter = nullptr) const
   {
     TRACE_SUBSET (this);
     const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
@@ -1742,9 +1744,12 @@ struct ClassDefFormat1
 
     hb_codepoint_t start = startGlyph;
     hb_codepoint_t end   = start + classValue.len;
+
     for (const hb_codepoint_t gid : + hb_range (start, end)
-				    | hb_filter (glyphset))
+                                    | hb_filter (glyphset))
     {
+      if (glyph_filter && !glyph_filter->has(gid)) continue;
+
       unsigned klass = classValue[gid - start];
       if (!klass) continue;
 
@@ -1753,8 +1758,12 @@ struct ClassDefFormat1
       orig_klasses.add (klass);
     }
 
-    ClassDef_remap_and_serialize (c->serializer, glyphset, gid_org_klass_map,
-				  glyphs, orig_klasses, klass_map);
+    unsigned glyph_count = glyph_filter
+                           ? hb_len (hb_iter (glyphset) | hb_filter (glyph_filter))
+                           : glyphset.get_population ();
+    use_class_zero = use_class_zero && glyph_count <= gid_org_klass_map.get_population ();
+    ClassDef_remap_and_serialize (c->serializer, gid_org_klass_map,
+				  glyphs, orig_klasses, use_class_zero, klass_map);
     return_trace ((bool) glyphs);
   }
 
@@ -1903,7 +1912,9 @@ struct ClassDefFormat2
   }
 
   bool subset (hb_subset_context_t *c,
-	       hb_map_t *klass_map = nullptr /*OUT*/) const
+	       hb_map_t *klass_map = nullptr /*OUT*/,
+               bool use_class_zero = true,
+               const Coverage* glyph_filter = nullptr) const
   {
     TRACE_SUBSET (this);
     const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
@@ -1923,14 +1934,19 @@ struct ClassDefFormat2
       for (hb_codepoint_t g = start; g < end; g++)
       {
 	if (!glyphset.has (g)) continue;
+        if (glyph_filter && !glyph_filter->has (g)) continue;
 	glyphs.push (glyph_map[g]);
 	gid_org_klass_map.set (glyph_map[g], klass);
 	orig_klasses.add (klass);
       }
     }
 
-    ClassDef_remap_and_serialize (c->serializer, glyphset, gid_org_klass_map,
-				  glyphs, orig_klasses, klass_map);
+    unsigned glyph_count = glyph_filter
+                           ? hb_len (hb_iter (glyphset) | hb_filter (glyph_filter))
+                           : glyphset.get_population ();
+    use_class_zero = use_class_zero && glyph_count <= gid_org_klass_map.get_population ();
+    ClassDef_remap_and_serialize (c->serializer, gid_org_klass_map,
+				  glyphs, orig_klasses, use_class_zero, klass_map);
     return_trace ((bool) glyphs);
   }
 
@@ -2045,10 +2061,9 @@ struct ClassDef
     if (likely (it))
     {
       hb_codepoint_t glyph_min = (*it).first;
-      hb_codepoint_t glyph_max = + it
-				 | hb_map (hb_first)
-				 | hb_reduce (hb_max, 0u);
+      hb_codepoint_t glyph_max = glyph_min;
 
+      unsigned num_glyphs = 0;
       unsigned num_ranges = 1;
       hb_codepoint_t prev_gid = glyph_min;
       unsigned prev_klass = (*it).second;
@@ -2057,7 +2072,9 @@ struct ClassDef
       {
 	hb_codepoint_t cur_gid = gid_klass_pair.first;
 	unsigned cur_klass = gid_klass_pair.second;
+        if (cur_klass) num_glyphs++;
 	if (cur_gid == glyph_min || !cur_klass) continue;
+        if (cur_gid > glyph_max) glyph_max = cur_gid;
 	if (cur_gid != prev_gid + 1 ||
 	    cur_klass != prev_klass)
 	  num_ranges++;
@@ -2066,7 +2083,7 @@ struct ClassDef
 	prev_klass = cur_klass;
       }
 
-      if (1 + (glyph_max - glyph_min + 1) <= num_ranges * 3)
+      if (num_glyphs && 1 + (glyph_max - glyph_min + 1) <= num_ranges * 3)
 	format = 1;
     }
     u.format = format;
@@ -2080,12 +2097,14 @@ struct ClassDef
   }
 
   bool subset (hb_subset_context_t *c,
-	       hb_map_t *klass_map = nullptr /*OUT*/) const
+	       hb_map_t *klass_map = nullptr /*OUT*/,
+               bool use_class_zero = true,
+               const Coverage* glyph_filter = nullptr) const
   {
     TRACE_SUBSET (this);
     switch (u.format) {
-    case 1: return_trace (u.format1.subset (c, klass_map));
-    case 2: return_trace (u.format2.subset (c, klass_map));
+    case 1: return_trace (u.format1.subset (c, klass_map, use_class_zero, glyph_filter));
+    case 2: return_trace (u.format2.subset (c, klass_map, use_class_zero, glyph_filter));
     default:return_trace (false);
     }
   }
diff --git a/src/hb-ot-layout-gpos-table.hh b/src/hb-ot-layout-gpos-table.hh
index f523e35c0..85ff4bc84 100644
--- a/src/hb-ot-layout-gpos-table.hh
+++ b/src/hb-ot-layout-gpos-table.hh
@@ -1358,7 +1358,7 @@ struct PairPosFormat2
     if ((!valueFormat1.has_device ()) && (!valueFormat2.has_device ())) return;
 
     hb_set_t class1_set, class2_set;
-    for (const unsigned cp : c->glyph_set->iter ())
+    for (const unsigned cp : + c->glyph_set->iter () | hb_filter (this + coverage))
     {
       unsigned klass1 = (this+classDef1).get (cp);
       unsigned klass2 = (this+classDef2).get (cp);
@@ -1366,7 +1366,10 @@ struct PairPosFormat2
       class2_set.add (klass2);
     }
 
-    if (class1_set.is_empty () || class2_set.is_empty ()) return;
+    if (class1_set.is_empty ()
+        || class2_set.is_empty ()
+        || (class2_set.get_population() == 1 && class2_set.has(0)))
+      return;
 
     unsigned len1 = valueFormat1.get_len ();
     unsigned len2 = valueFormat2.get_len ();
@@ -1435,11 +1438,11 @@ struct PairPosFormat2
     out->valueFormat2 = valueFormat2;
 
     hb_map_t klass1_map;
-    out->classDef1.serialize_subset (c, classDef1, this, &klass1_map);
+    out->classDef1.serialize_subset (c, classDef1, this, &klass1_map, true, &(this + coverage));
     out->class1Count = klass1_map.get_population ();
 
     hb_map_t klass2_map;
-    out->classDef2.serialize_subset (c, classDef2, this, &klass2_map);
+    out->classDef2.serialize_subset (c, classDef2, this, &klass2_map, false);
     out->class2Count = klass2_map.get_population ();
 
     unsigned len1 = valueFormat1.get_len ();
diff --git a/test/api/fonts/AdobeVFPrototype.WA.gpos.otf b/test/api/fonts/AdobeVFPrototype.WA.gpos.otf
index 967ef2554..31c9970fd 100644
Binary files a/test/api/fonts/AdobeVFPrototype.WA.gpos.otf and b/test/api/fonts/AdobeVFPrototype.WA.gpos.otf differ
diff --git a/test/api/fonts/Roboto-Regular-gpos-aw.ttf b/test/api/fonts/Roboto-Regular-gpos-aw.ttf
index 1b34d0551..8dfa99a1b 100644
Binary files a/test/api/fonts/Roboto-Regular-gpos-aw.ttf and b/test/api/fonts/Roboto-Regular-gpos-aw.ttf differ
diff --git a/test/api/test-subset-gpos.c b/test/api/test-subset-gpos.c
index 5c2fe2ed0..e1b3d0091 100644
--- a/test/api/test-subset-gpos.c
+++ b/test/api/test-subset-gpos.c
@@ -32,7 +32,6 @@
 static void
 test_subset_gpos_lookup_subtable (void)
 {
-#ifdef HB_EXPERIMENTAL_API
   hb_face_t *face_pwa = hb_test_open_font_file ("fonts/Roboto-Regular-gpos-.aw.ttf");
   hb_face_t *face_wa = hb_test_open_font_file ("fonts/Roboto-Regular-gpos-aw.ttf");
 
@@ -53,14 +52,11 @@ test_subset_gpos_lookup_subtable (void)
   hb_face_destroy (face_pwa_subset);
   hb_face_destroy (face_pwa);
   hb_face_destroy (face_wa);
-#endif
 }
 
-/* TODO: Once GDEF subsetting is implemented, this test may fail & expected result need update. */
 static void
 test_subset_gpos_pairpos1_vf (void)
 {
-#ifdef HB_EXPERIMENTAL_API
   hb_face_t *face_wav = hb_test_open_font_file ("fonts/AdobeVFPrototype.WAV.gpos.otf");
   hb_face_t *face_wa = hb_test_open_font_file ("fonts/AdobeVFPrototype.WA.gpos.otf");
 
@@ -81,7 +77,6 @@ test_subset_gpos_pairpos1_vf (void)
   hb_face_destroy (face_wav_subset);
   hb_face_destroy (face_wav);
   hb_face_destroy (face_wa);
-#endif
 }
 
 int
diff --git a/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41,42,43,57.otf b/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41,42,43,57.otf
index cf686c366..f46824945 100644
Binary files a/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41,42,43,57.otf and b/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41,42,43,57.otf differ
diff --git a/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41,42,43.otf b/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41,42,43.otf
index dc41ad4b1..ff8afb9a7 100644
Binary files a/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41,42,43.otf and b/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41,42,43.otf differ
diff --git a/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41,42.otf b/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41,42.otf
index 749daaf4d..5e81cb486 100644
Binary files a/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41,42.otf and b/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41,42.otf differ
diff --git a/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41,56,57.otf b/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41,56,57.otf
index a178115b4..04dfad564 100644
Binary files a/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41,56,57.otf and b/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41,56,57.otf differ
diff --git a/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41.otf b/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41.otf
index 96374c4b7..5c166ed64 100644
Binary files a/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41.otf and b/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.41.otf differ
diff --git a/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.42,57.otf b/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.42,57.otf
index e17e1ec73..43a416592 100644
Binary files a/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.42,57.otf and b/test/subset/data/expected/layout.gdef-varstore/AdobeVFPrototype.keep-gdef-gpos.42,57.otf differ
diff --git a/test/subset/data/expected/layout.gdef/Roboto-Regular.keep-gdef-gpos.1E00,303.ttf b/test/subset/data/expected/layout.gdef/Roboto-Regular.keep-gdef-gpos.1E00,303.ttf
index b7411bb4d..a398c6f96 100644
Binary files a/test/subset/data/expected/layout.gdef/Roboto-Regular.keep-gdef-gpos.1E00,303.ttf and b/test/subset/data/expected/layout.gdef/Roboto-Regular.keep-gdef-gpos.1E00,303.ttf differ
diff --git a/test/subset/data/expected/layout.gdef/Roboto-Regular.keep-gdef-gpos.41,42,43.ttf b/test/subset/data/expected/layout.gdef/Roboto-Regular.keep-gdef-gpos.41,42,43.ttf
index 0ad253258..fcfc584b7 100644
Binary files a/test/subset/data/expected/layout.gdef/Roboto-Regular.keep-gdef-gpos.41,42,43.ttf and b/test/subset/data/expected/layout.gdef/Roboto-Regular.keep-gdef-gpos.41,42,43.ttf differ
diff --git a/test/subset/data/expected/layout.gpos2/gpos2_1_font7.keep-layout-retain-gids.2E,23.otf b/test/subset/data/expected/layout.gpos2/gpos2_1_font7.keep-layout-retain-gids.2E,23.otf
new file mode 100644
index 000000000..849a7c5b1
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diff --git a/test/subset/data/expected/layout.gpos2/gpos2_1_font7.keep-layout.2E,23.otf b/test/subset/data/expected/layout.gpos2/gpos2_1_font7.keep-layout.2E,23.otf
new file mode 100644
index 000000000..7ffd4689a
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diff --git a/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout-retain-gids.21,23,25.otf b/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout-retain-gids.21,23,25.otf
index b34a49fa0..77c408cd1 100644
Binary files a/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout-retain-gids.21,23,25.otf and b/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout-retain-gids.21,23,25.otf differ
diff --git a/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout-retain-gids.21,23.otf b/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout-retain-gids.21,23.otf
index 2ad1d293d..9abdd3204 100644
Binary files a/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout-retain-gids.21,23.otf and b/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout-retain-gids.21,23.otf differ
diff --git a/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout-retain-gids.2E,23.otf b/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout-retain-gids.2E,23.otf
new file mode 100644
index 000000000..786de3028
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diff --git a/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout-retain-gids.41,42,43.otf b/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout-retain-gids.41,42,43.otf
index 5d9fe7725..1fb3d12e8 100644
Binary files a/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout-retain-gids.41,42,43.otf and b/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout-retain-gids.41,42,43.otf differ
diff --git a/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout-retain-gids.retain-all-codepoint.otf b/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout-retain-gids.retain-all-codepoint.otf
index 88e60461c..aebc39673 100644
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diff --git a/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout.21,23,25.otf b/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout.21,23,25.otf
index 195c8dc32..f227d5ad6 100644
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diff --git a/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout.21,23.otf b/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout.21,23.otf
index d10d3621b..a785d4967 100644
Binary files a/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout.21,23.otf and b/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout.21,23.otf differ
diff --git a/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout.2E,23.otf b/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout.2E,23.otf
new file mode 100644
index 000000000..a80ccfcbc
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diff --git a/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout.41,42,43.otf b/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout.41,42,43.otf
index 83e2e61da..3766e7f65 100644
Binary files a/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout.41,42,43.otf and b/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout.41,42,43.otf differ
diff --git a/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout.retain-all-codepoint.otf b/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout.retain-all-codepoint.otf
index 88e60461c..aebc39673 100644
Binary files a/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout.retain-all-codepoint.otf and b/test/subset/data/expected/layout.gpos2/gpos2_2_font5.keep-layout.retain-all-codepoint.otf differ
diff --git a/test/subset/data/expected/layout.gpos8.amiri/Amiri-Regular.keep-layout-retain-gids.627,644,623,62D,644,627,645,2E.ttf b/test/subset/data/expected/layout.gpos8.amiri/Amiri-Regular.keep-layout-retain-gids.627,644,623,62D,644,627,645,2E.ttf
index f361131df..7ae9c56be 100644
Binary files a/test/subset/data/expected/layout.gpos8.amiri/Amiri-Regular.keep-layout-retain-gids.627,644,623,62D,644,627,645,2E.ttf and b/test/subset/data/expected/layout.gpos8.amiri/Amiri-Regular.keep-layout-retain-gids.627,644,623,62D,644,627,645,2E.ttf differ
diff --git a/test/subset/data/expected/layout.gpos8.amiri/Amiri-Regular.keep-layout.627,644,623,62D,644,627,645,2E.ttf b/test/subset/data/expected/layout.gpos8.amiri/Amiri-Regular.keep-layout.627,644,623,62D,644,627,645,2E.ttf
index 57ef1910e..3a64b97a6 100644
Binary files a/test/subset/data/expected/layout.gpos8.amiri/Amiri-Regular.keep-layout.627,644,623,62D,644,627,645,2E.ttf and b/test/subset/data/expected/layout.gpos8.amiri/Amiri-Regular.keep-layout.627,644,623,62D,644,627,645,2E.ttf differ
diff --git a/test/subset/data/fonts/gpos2_2_font5.otf b/test/subset/data/fonts/gpos2_2_font5.otf
index 63af3bca1..19833cf8f 100644
Binary files a/test/subset/data/fonts/gpos2_2_font5.otf and b/test/subset/data/fonts/gpos2_2_font5.otf differ
diff --git a/test/subset/data/tests/layout.gpos2.tests b/test/subset/data/tests/layout.gpos2.tests
index 5d3a0bb6e..08799946b 100644
--- a/test/subset/data/tests/layout.gpos2.tests
+++ b/test/subset/data/tests/layout.gpos2.tests
@@ -9,5 +9,6 @@ keep-layout-retain-gids.txt
 SUBSETS:
 !#
 !#%
+.#
 ABC
 *