diff --git a/src/hb-open-type.hh b/src/hb-open-type.hh
index a22b62353..276ec9c39 100644
--- a/src/hb-open-type.hh
+++ b/src/hb-open-type.hh
@@ -504,7 +504,7 @@ struct UnsizedArrayOf
   bool serialize (hb_serialize_context_t *c, Iterator items)
   {
     TRACE_SERIALIZE (this);
-    unsigned count = items.len ();
+    unsigned count = hb_len (items);
     if (unlikely (!serialize (c, count, false))) return_trace (false);
     /* TODO Umm. Just exhaust the iterator instead?  Being extra
      * cautious right now.. */
@@ -678,7 +678,7 @@ struct ArrayOf
   HB_NODISCARD bool serialize (hb_serialize_context_t *c, Iterator items)
   {
     TRACE_SERIALIZE (this);
-    unsigned count = items.len ();
+    unsigned count = hb_len (items);
     if (unlikely (!serialize (c, count, false))) return_trace (false);
     /* TODO Umm. Just exhaust the iterator instead?  Being extra
      * cautious right now.. */
@@ -840,7 +840,7 @@ struct HeadlessArrayOf
   HB_NODISCARD bool serialize (hb_serialize_context_t *c, Iterator items)
   {
     TRACE_SERIALIZE (this);
-    unsigned count = items.len ();
+    unsigned count = hb_len (items);
     if (unlikely (!serialize (c, count, false))) return_trace (false);
     /* TODO Umm. Just exhaust the iterator instead?  Being extra
      * cautious right now.. */