diff --git a/src/hb-vector.hh b/src/hb-vector.hh
index f8640fd95..8748f8d44 100644
--- a/src/hb-vector.hh
+++ b/src/hb-vector.hh
@@ -55,10 +55,7 @@ struct hb_vector_t
 	    hb_requires (hb_is_iterable (Iterable))>
   hb_vector_t (const Iterable &o) : hb_vector_t ()
   {
-    auto iter = hb_iter (o);
-    if (iter.is_random_access_iterator || iter.has_fast_len)
-      alloc (hb_len (iter), true);
-    hb_copy (iter, *this);
+    extend (o);
   }
   template <typename Iterable,
 	    hb_requires (hb_is_iterable (Iterable))>