diff --git a/simplify/loops.ml b/simplify/loops.ml
index 5125e44ea72119af660c42b59a70c96baee06c0d..c2ff355f0624f9e63a6569ecef1ec9c0cf160ea3 100644
--- a/simplify/loops.ml
+++ b/simplify/loops.ml
@@ -71,7 +71,7 @@ let bounds_from_list l =
   let bounds = new_bounds () in
   List.iter (fun (lid,bound) ->
       let lname = lname_from_lid lid in
-      Hashtbl.add bounds lname bound) l;
+      Hashtbl.replace bounds lname bound) l;
   bounds
   
 open Format