diff --git a/src/graph/graph.hh b/src/graph/graph.hh
index 347a2b012..a69deb00a 100644
--- a/src/graph/graph.hh
+++ b/src/graph/graph.hh
@@ -61,12 +61,32 @@ struct graph_t
       }
     }
 
-    bool equals (const vertex_t& other, const graph_t& graph) const
+    bool equals (const vertex_t& other,
+                 const graph_t& graph,
+                 const graph_t& other_graph,
+                 unsigned depth) const
     {
       if (!(as_bytes () == other.as_bytes ()))
-        return false;
+      {
+        DEBUG_MSG (SUBSET_REPACK, nullptr,
+                   "vertex [%lu] bytes != [%lu] bytes, depth = %u",
+                   table_size (),
+                   other.table_size (),
+                   depth);
 
-      return links_equal (graph, obj.real_links, other.obj.real_links);
+        auto a = as_bytes ();
+        auto b = other.as_bytes ();
+        while (a || b)
+        {
+          DEBUG_MSG (SUBSET_REPACK, nullptr,
+                     "  0x%x %s 0x%x", *a, (*a == *b) ? "==" : "!=", *b);
+          a++;
+          b++;
+        }
+        return false;
+      }
+
+      return links_equal (obj.real_links, other.obj.real_links, graph, other_graph, depth);
     }
 
     hb_bytes_t as_bytes () const
@@ -194,9 +214,11 @@ struct graph_t
     }
 
    private:
-    bool links_equal (const graph_t& graph,
-                      const hb_vector_t<hb_serialize_context_t::object_t::link_t>& this_links,
-                      const hb_vector_t<hb_serialize_context_t::object_t::link_t>& other_links) const
+    bool links_equal (const hb_vector_t<hb_serialize_context_t::object_t::link_t>& this_links,
+                      const hb_vector_t<hb_serialize_context_t::object_t::link_t>& other_links,
+                      const graph_t& graph,
+                      const graph_t& other_graph,
+                      unsigned depth) const
     {
       auto a = this_links.iter ();
       auto b = other_links.iter ();
@@ -213,7 +235,8 @@ struct graph_t
             link_a.bias != link_b.bias)
           return false;
 
-        if (!graph.vertices_[link_a.objidx].equals (graph.vertices_[link_b.objidx], graph))
+        if (!graph.vertices_[link_a.objidx].equals (
+                other_graph.vertices_[link_b.objidx], graph, other_graph, depth + 1))
           return false;
 
         a++;
@@ -293,7 +316,7 @@ struct graph_t
 
   bool operator== (const graph_t& other) const
   {
-    return root ().equals (other.root (), *this);
+    return root ().equals (other.root (), *this, other, 0);
   }
 
   // Sorts links of all objects in a consistent manner and zeroes all offsets.
diff --git a/src/graph/markbasepos-graph.hh b/src/graph/markbasepos-graph.hh
index 390bc7249..69f8fc72b 100644
--- a/src/graph/markbasepos-graph.hh
+++ b/src/graph/markbasepos-graph.hh
@@ -158,7 +158,8 @@ struct MarkArray : public OT::Layout::GPOS_impl::MarkArray
   unsigned clone (gsubgpos_graph_context_t& c,
                   unsigned this_index,
                   const hb_hashmap_t<unsigned, unsigned>& pos_to_index,
-                  hb_set_t& marks)
+                  hb_set_t& marks,
+                  unsigned start_class)
   {
     unsigned size = MarkArray::min_size +
                     OT::Layout::GPOS_impl::MarkRecord::static_size *
@@ -172,7 +173,7 @@ struct MarkArray : public OT::Layout::GPOS_impl::MarkArray
     unsigned i = 0;
     for (hb_codepoint_t mark : marks)
     {
-      (*prime)[i].klass = (*this)[mark].klass;
+      (*prime)[i].klass = (*this)[mark].klass - start_class;
       unsigned offset_pos = (char*) &((*this)[mark].markAnchor) - (char*) this;
       unsigned* anchor_index;
       if (pos_to_index.has (offset_pos, &anchor_index))
@@ -433,7 +434,8 @@ struct MarkBasePosFormat1 : public OT::Layout::GPOS_impl::MarkBasePosFormat1_2<S
         mark_array.table->clone (sc.c,
                                  mark_array.index,
                                  sc.mark_array_links,
-                                 marks);
+                                 marks,
+                                 start);
     graph.add_link (&(prime->markArray), prime_id, new_mark_array);
 
     auto base_array =
diff --git a/src/test-repacker.cc b/src/test-repacker.cc
index bc3cc3f1a..9ab328047 100644
--- a/src/test-repacker.cc
+++ b/src/test-repacker.cc
@@ -177,6 +177,16 @@ static unsigned add_coverage (unsigned start, unsigned end,
   return add_object ((char*) coverage, 10, c);
 }
 
+
+template<typename It>
+static unsigned add_coverage (It it,
+                              hb_serialize_context_t* c)
+{
+  c->push ();
+  OT::Layout::Common::Coverage_serialize (c, it);
+  return c->pop_pack (false);
+}
+
 // Adds a class that maps glyphs from [start_glyph, end_glyph)
 // to classes 1...n
 static unsigned add_class_def (uint16_t start_glyph,
@@ -384,20 +394,27 @@ struct MarkBasePosBuffers
       (uint8_t) (num_marks & 0xFF),
     };
     start_object ((char*) mark_count_buffer, 2, c);
-    for (unsigned i = 0; i < num_marks; i++)
+    for (unsigned mark = 0; mark < mark_count; mark++)
     {
-      unsigned klass = i % class_per_table;
-      extend ((char*) &class_buffer[2 * klass], 2, c);
+      unsigned klass = mark % class_count;
+      if (klass < start_class || klass > end_class) continue;
+      klass -= start_class;
 
-      unsigned mark = table_index * num_marks + i;
+      extend ((char*) &class_buffer[2 * klass], 2, c);
       add_offset (mark_anchors[mark], c);
     }
     unsigned mark_array = c->pop_pack (false);
 
     // markCoverage
-    unsigned mark_coverage = add_coverage (num_marks * table_index,
-                                           num_marks * (table_index + 1) - 1,
-                                           c);
+    auto it =
+        + hb_range ((hb_codepoint_t) mark_count)
+        | hb_filter ([&] (hb_codepoint_t mark) {
+          unsigned klass = mark % class_count;
+          return klass >= class_per_table * table_index &&
+              klass < class_per_table * (table_index + 1);
+        })
+        ;
+    unsigned mark_coverage = add_coverage (it, c);
 
     // baseCoverage
     unsigned base_coverage = add_coverage (10, 10 + base_count - 1, c);
@@ -406,7 +423,7 @@ struct MarkBasePosBuffers
                                 base_coverage,
                                 mark_array,
                                 base_array,
-                                class_count,
+                                class_per_table,
                                 c);
   }
 };