diff --git a/lib/sasacore/sasa.ml b/lib/sasacore/sasa.ml
index 16649572e18952a2ee6d76d35ee2034cc905f84f..b598862cf0f51358ca4044b11a96413ebc29d6b5 100644
--- a/lib/sasacore/sasa.ml
+++ b/lib/sasacore/sasa.ml
@@ -1,4 +1,4 @@
-(* Time-stamp: <modified the 18/03/2019 (at 09:21) by Erwan Jahier> *)
+(* Time-stamp: <modified the 20/03/2019 (at 12:09) by Erwan Jahier> *)
 
 (* XXX Je pourrais utiliser Lwt pour rendre step non-bloquant, ce qui
    permettrait d'accelerer la simu sur les machines qui ont plusieurs
@@ -170,7 +170,8 @@ let (make : string array -> t) =
     if args.gen_lutin then (
       let fn = (Filename.remove_extension args.topo) ^ ".lut" in
       if Sys.file_exists fn then (
-        Printf.eprintf "%s already exists.\n" fn; flush stderr
+        Printf.eprintf "%s already exists: rename it to proceed.\n" fn;
+        flush stderr; exit 1
       ) else 
         let oc = open_out fn in
         Printf.fprintf oc "%s" (GenLutin.f pl);