diff --git a/src/hb-open-type.hh b/src/hb-open-type.hh
index ccbbec517..a22b62353 100644
--- a/src/hb-open-type.hh
+++ b/src/hb-open-type.hh
@@ -493,10 +493,10 @@ struct UnsizedArrayOf
   void qsort (unsigned int len, unsigned int start = 0, unsigned int end = (unsigned int) -1)
   { as_array (len).qsort (start, end); }
 
-  bool serialize (hb_serialize_context_t *c, unsigned int items_len)
+  bool serialize (hb_serialize_context_t *c, unsigned int items_len, bool clear = true)
   {
     TRACE_SERIALIZE (this);
-    if (unlikely (!c->extend (this, items_len))) return_trace (false);
+    if (unlikely (!c->extend_size (this, get_size (items_len), clear))) return_trace (false);
     return_trace (true);
   }
   template <typename Iterator,
@@ -505,7 +505,7 @@ struct UnsizedArrayOf
   {
     TRACE_SERIALIZE (this);
     unsigned count = items.len ();
-    if (unlikely (!serialize (c, count))) return_trace (false);
+    if (unlikely (!serialize (c, count, false))) return_trace (false);
     /* TODO Umm. Just exhaust the iterator instead?  Being extra
      * cautious right now.. */
     for (unsigned i = 0; i < count; i++, ++items)
@@ -665,12 +665,12 @@ struct ArrayOf
   void qsort ()
   { as_array ().qsort (); }
 
-  HB_NODISCARD bool serialize (hb_serialize_context_t *c, unsigned items_len)
+  HB_NODISCARD bool serialize (hb_serialize_context_t *c, unsigned items_len, bool clear = true)
   {
     TRACE_SERIALIZE (this);
     if (unlikely (!c->extend_min (this))) return_trace (false);
     c->check_assign (len, items_len, HB_SERIALIZE_ERROR_ARRAY_OVERFLOW);
-    if (unlikely (!c->extend (this))) return_trace (false);
+    if (unlikely (!c->extend_size (this, get_size (), clear))) return_trace (false);
     return_trace (true);
   }
   template <typename Iterator,
@@ -679,7 +679,7 @@ struct ArrayOf
   {
     TRACE_SERIALIZE (this);
     unsigned count = items.len ();
-    if (unlikely (!serialize (c, count))) return_trace (false);
+    if (unlikely (!serialize (c, count, false))) return_trace (false);
     /* TODO Umm. Just exhaust the iterator instead?  Being extra
      * cautious right now.. */
     for (unsigned i = 0; i < count; i++, ++items)
@@ -827,21 +827,21 @@ struct HeadlessArrayOf
   const Type *begin () const { return arrayZ; }
   const Type *end () const { return arrayZ + get_length (); }
 
-  bool serialize (hb_serialize_context_t *c, unsigned int items_len)
+  HB_NODISCARD bool serialize (hb_serialize_context_t *c, unsigned int items_len, bool clear = true)
   {
     TRACE_SERIALIZE (this);
     if (unlikely (!c->extend_min (this))) return_trace (false);
     c->check_assign (lenP1, items_len + 1, HB_SERIALIZE_ERROR_ARRAY_OVERFLOW);
-    if (unlikely (!c->extend (this))) return_trace (false);
+    if (unlikely (!c->extend_size (this, get_size (), clear))) return_trace (false);
     return_trace (true);
   }
   template <typename Iterator,
 	    hb_requires (hb_is_source_of (Iterator, Type))>
-  bool serialize (hb_serialize_context_t *c, Iterator items)
+  HB_NODISCARD bool serialize (hb_serialize_context_t *c, Iterator items)
   {
     TRACE_SERIALIZE (this);
     unsigned count = items.len ();
-    if (unlikely (!serialize (c, count))) return_trace (false);
+    if (unlikely (!serialize (c, count, false))) return_trace (false);
     /* TODO Umm. Just exhaust the iterator instead?  Being extra
      * cautious right now.. */
     for (unsigned i = 0; i < count; i++, ++items)