diff --git a/src/hb-iter.hh b/src/hb-iter.hh
index 79ff316aa..981c5c218 100644
--- a/src/hb-iter.hh
+++ b/src/hb-iter.hh
@@ -572,7 +572,7 @@ struct hb_zip_iter_t :
   B b;
 };
 struct
-{
+{ HB_PARTIALIZE(2);
   template <typename A, typename B,
 	    hb_requires (hb_is_iterable (A) && hb_is_iterable (B))>
   hb_zip_iter_t<hb_iter_type<A>, hb_iter_type<B>>