diff --git a/demo_ref.eliom b/demo_ref.eliom
index c7eb5b1..78b559f 100644
--- a/demo_ref.eliom
+++ b/demo_ref.eliom
@@ -10,7 +10,8 @@ open%shared Eliom.Content.Html.F
    Ocsigen Start is creating a session group for each user.
 *)
 let%server last_visit =
-  Eliom.Reference.eref ~persistent:"demo_last_visit"
+  Eliom.Reference.eref
+    ~persistent:("demo_last_visit", [%json: Os.Date.local_calendar option])
     ~scope:Eliom.Common.default_group_scope None
 
 (* Read & reset last_visit *)
diff --git a/tools/gen_dune.ml b/tools/gen_dune.ml
index 9a2d8f1..c1fb399 100644
--- a/tools/gen_dune.ml
+++ b/tools/gen_dune.ml
@@ -23,7 +23,33 @@ let handle_file_client nm =
       nm nm
 
 let () =
-  Array.concat (List.map Sys.readdir [".."; "../assets"])
+  let root = Sys.readdir ".." in
+  let assets = Sys.readdir "../assets" in
+  (* The build directory mirrors the sources but also holds generated files,
+     which must not be enumerated or their client rule would be emitted twice:
+     - .pp.eliom/.pp.eliomi: preprocessing artifacts;
+     - the i18n modules produced from assets/*.tsv (the .tsv already emits the
+       rule) and the static config produced from *.eliom.in. *)
+  let generated_eliom = Hashtbl.create 16 in
+  Array.iter
+    (fun nm ->
+       if Filename.check_suffix nm ".tsv"
+       then Hashtbl.replace generated_eliom (Filename.chop_suffix nm ".tsv") ())
+    assets;
+  Array.iter
+    (fun nm ->
+       if Filename.check_suffix nm ".eliom.in"
+       then
+         Hashtbl.replace generated_eliom (Filename.chop_suffix nm ".eliom.in") ())
+    root;
+  let is_generated nm =
+    Filename.check_suffix nm ".pp.eliom"
+    || Filename.check_suffix nm ".pp.eliomi"
+    || (Filename.check_suffix nm ".eliom"
+       && Hashtbl.mem generated_eliom (Filename.chop_suffix nm ".eliom"))
+  in
+  Array.concat [root; assets]
   |> Array.to_list |> List.sort compare
   |> List.filter (fun nm -> nm.[0] <> '.')
+  |> List.filter (fun nm -> not (is_generated nm))
   |> List.iter handle_file_client