diff --git a/src/cmap.ml b/src/cmap.ml
index 69f447b..3afb2b6 100644
--- a/src/cmap.ml
+++ b/src/cmap.ml
@@ -173,6 +173,12 @@ end = struct
   let of_list_with_key_multi list ~get_key =
     Using_comparator.of_list_with_key_multi ~comparator list ~get_key
 
+  let of_list_with_key_fold list ~get_key ~init ~f =
+    failwith "Map.of_list_with_key_fold: not implemented yet"
+
+  let of_list_with_key_reduce list ~get_key ~f =
+    failwith "Map.of_list_with_key_reduce: not implemented yet"
+
   let of_alist alist = Using_comparator.of_alist ~comparator alist
 
   let of_alist_or_error alist = Using_comparator.of_alist_or_error ~comparator alist