diff --git a/src/hb-ot-layout-gsub-table.hh b/src/hb-ot-layout-gsub-table.hh
index 25b61176b..25656c951 100644
--- a/src/hb-ot-layout-gsub-table.hh
+++ b/src/hb-ot-layout-gsub-table.hh
@@ -289,9 +289,7 @@ struct SingleSubst
   } u;
 };
 
-template<typename Iterator,
-    	 hb_requires (hb_is_sorted_source_of (Iterator,
-                                              const hb_codepoint_pair_t))>
+template<typename Iterator>
 static inline void
 SingleSubst_serialize (hb_serialize_context_t *c,
 		       Iterator it)