diff --git a/src/graph/gsubgpos-context.cc b/src/graph/gsubgpos-context.cc
index f71c73aa1..e0ff6ff85 100644
--- a/src/graph/gsubgpos-context.cc
+++ b/src/graph/gsubgpos-context.cc
@@ -29,22 +29,33 @@
 namespace graph {
 
 gsubgpos_graph_context_t::gsubgpos_graph_context_t (hb_tag_t table_tag_,
-                                                    graph_t& graph_,
-                                                    hb_vector_t<char>& buffer_)
+                                                    graph_t& graph_)
     : table_tag (table_tag_),
       graph (graph_),
-      buffer (buffer_),
       lookup_list_index (0),
-      lookups ()
+      lookups (),
+      buffers ()
 {
+  if (table_tag_ != HB_OT_TAG_GPOS
+      &&  table_tag_ != HB_OT_TAG_GSUB)
+    return;
+
   GSTAR* gstar = graph::GSTAR::graph_to_gstar (graph_);
   if (gstar) {
     gstar->find_lookups (graph, lookups);
     lookup_list_index = gstar->get_lookup_list_index (graph_);
   }
+}
 
-  unsigned extension_size = OT::ExtensionFormat1<OT::Layout::GSUB_impl::ExtensionSubst>::static_size;
-  buffer.alloc (num_non_ext_subtables () * extension_size);
+unsigned gsubgpos_graph_context_t::create_node (unsigned size)
+{
+  char* buffer = (char*) hb_calloc (1, size);
+  if (!buffer)
+    return -1;
+
+  buffers.push (buffer);
+
+  return graph.new_node (buffer, buffer + size);
 }
 
 unsigned gsubgpos_graph_context_t::num_non_ext_subtables ()  {
diff --git a/src/graph/gsubgpos-context.hh b/src/graph/gsubgpos-context.hh
index ff8f29e0d..89649f197 100644
--- a/src/graph/gsubgpos-context.hh
+++ b/src/graph/gsubgpos-context.hh
@@ -38,19 +38,21 @@ struct gsubgpos_graph_context_t
 {
   hb_tag_t table_tag;
   graph_t& graph;
-  hb_vector_t<char>& buffer;
   unsigned lookup_list_index;
   hb_hashmap_t<unsigned, graph::Lookup*> lookups;
+  hb_vector_t<char*> buffers;
 
   HB_INTERNAL gsubgpos_graph_context_t (hb_tag_t table_tag_,
-                                        graph_t& graph_,
-                                        hb_vector_t<char>& buffer_);
+                                        graph_t& graph_);
 
-  bool in_error () const
+  ~gsubgpos_graph_context_t ()
   {
-    return buffer.in_error ();
+    for (char* b : buffers)
+      hb_free (b);
   }
 
+  HB_INTERNAL unsigned create_node (unsigned size);
+
  private:
   HB_INTERNAL unsigned num_non_ext_subtables ();
 };
diff --git a/src/graph/gsubgpos-graph.hh b/src/graph/gsubgpos-graph.hh
index 8d6e3a343..d35ea8df3 100644
--- a/src/graph/gsubgpos-graph.hh
+++ b/src/graph/gsubgpos-graph.hh
@@ -148,17 +148,16 @@ struct Lookup : public OT::Lookup
   {
     unsigned type = lookupType;
     unsigned extension_size = OT::ExtensionFormat1<OT::Layout::GSUB_impl::ExtensionSubst>::static_size;
-    unsigned start = c.buffer.length;
-    unsigned end = start + extension_size;
-    if (!c.buffer.resize (c.buffer.length + extension_size))
+
+
+    unsigned ext_index = c.create_node (extension_size);
+    if (ext_index == (unsigned) -1)
       return false;
 
     ExtensionFormat1<OT::Layout::GSUB_impl::ExtensionSubst>* extension =
-        (ExtensionFormat1<OT::Layout::GSUB_impl::ExtensionSubst>*) &c.buffer[start];
+        (ExtensionFormat1<OT::Layout::GSUB_impl::ExtensionSubst>*) c.graph.object (ext_index).head;
     extension->reset (type);
 
-    unsigned ext_index = c.graph.new_node (&c.buffer.arrayZ[start],
-                                           &c.buffer.arrayZ[end]);
     if (ext_index == (unsigned) -1) return false;
 
     auto& lookup_vertex = c.graph.vertices_[lookup_index];
diff --git a/src/hb-repacker.hh b/src/hb-repacker.hh
index 31dfa0862..1ee5985be 100644
--- a/src/hb-repacker.hh
+++ b/src/hb-repacker.hh
@@ -307,18 +307,13 @@ hb_resolve_overflows (const T& packed,
     return graph::serialize (sorted_graph);
   }
 
-  hb_vector_t<char> extension_buffer; // Needs to live until serialization is done.
-
+  graph::gsubgpos_graph_context_t ext_context (table_tag, sorted_graph);
   if ((table_tag == HB_OT_TAG_GPOS
        ||  table_tag == HB_OT_TAG_GSUB)
       && will_overflow)
   {
     if (recalculate_extensions)
     {
-      graph::gsubgpos_graph_context_t ext_context (table_tag, sorted_graph, extension_buffer);
-      if (ext_context.in_error ())
-        return nullptr;
-
       if (!_presplit_subtables_if_needed (ext_context)) {
         DEBUG_MSG (SUBSET_REPACK, nullptr, "Subtable splitting failed.");
         return nullptr;