diff --git a/src/plugins/wp/ProverWhy3.ml b/src/plugins/wp/ProverWhy3.ml
index b97a388f6c93f06d8676f31e71270a5c3c1183b2..62935c0fd4e636d0ee8a65008939ed3f235f1cc8 100644
--- a/src/plugins/wp/ProverWhy3.ml
+++ b/src/plugins/wp/ProverWhy3.ml
@@ -1413,8 +1413,7 @@ let editor_command pconf =
 
 let scriptfile ~force ~ext wpo =
   let dir = Wp_parameters.get_session_dir ~force "interactive" in
-  let filenoext = Filepath.Normalized.concat dir wpo.Wpo.po_sid in
-  Filepath.Normalized.concat filenoext ext
+  Filepath.Normalized.concat dir (wpo.Wpo.po_sid ^ ext)
 
 let updatescript ~script driver task =
   let backup = Filepath.Normalized.concat script ".bak" in