diff --git a/tests.ml b/tests.ml
index 36641d1..bace213 100644
--- a/tests.ml
+++ b/tests.ml
@@ -8,6 +8,9 @@ let rec pp_list ?(sep=", ") pp_item formatter = function
   | x::[] -> pp_item formatter x
   | [] -> ()
 
+(** Set of integers *)
+module ISet = Set.Make(struct type t = int let compare = compare end)
+
 let _ =
   let l = [0;1;2;3;4;5;6] in
   let l' = Sequence.List.of_seq
@@ -23,9 +26,13 @@ let _ =
       (Sequence.Hashtbl.to_seq h))
   in
   let l3 = Sequence.List.of_seq (Sequence.rev (Sequence.Int.range ~start:0 ~stop:42)) in
+  let set = List.fold_left (fun set x -> ISet.add x set) ISet.empty [4;3;100;42] in
+  let s = (module ISet : Set.S with type elt = int and type t = ISet.t) in
+  let l4 = Sequence.List.of_seq (Sequence.Set.to_seq s set) in
   Format.printf "l=@[<h>[%a]@]@." (pp_list Format.pp_print_int) l;
   Format.printf "l'=@[<h>[%a]@]@." (pp_list Format.pp_print_int) l';
   Format.printf "l''=@[<h>[%a]@]@." (pp_list Format.pp_print_int) l'';
   Format.printf "l2=@[<h>[%a]@]@." (pp_list Format.pp_print_string) l2;
   Format.printf "l3=@[<h>[%a]@]@." (pp_list Format.pp_print_int) l3;
+  Format.printf "l4=@[<h>[%a]@]@." (pp_list Format.pp_print_int) l4;
   ()