diff --git a/lex.ml b/lex.ml
index d45c269..9b54735 100644
--- a/lex.ml
+++ b/lex.ml
@@ -38,24 +38,24 @@ let rec partition_while f seq : 'a Seq.t * 'a Seq.t =
 
 let tokenize (str : string) : tokens =
   let seq = String.to_seq str in
-  let rec aux seq =
+  let rec aux seq () =
     let open Token in
     match seq () with
-    | Seq.Nil -> Seq.empty
+    | Seq.Nil -> Seq.Nil
     | Seq.Cons (x, s) ->
       if is_whitespace x then
-        aux s (* skip whitespace *)
+        aux s () (* skip whitespace *)
       else if is_digit x then
         let n, s = partition_while is_num seq in
         let n = int_of_string @@ String.of_seq n in
-        Seq.cons (Int n) (aux s)
+        Seq.Cons (Int n, aux s)
       else if is_ident_start x then
         let id, s = partition_while is_ident seq in
         let id = String.of_seq id in
-        Seq.cons (Ident id) (aux s)
+        Seq.Cons (Ident id, aux s)
       else
         match find_token seq with
         | None -> raise Token_not_found
-        | Some (t, s) -> Seq.cons t (aux s)
+        | Some (t, s) -> Seq.Cons (t, aux s)
   in
   aux seq