diff --git a/src/ace-lib/ace.ml b/src/ace-lib/ace.ml
index 2bbe01e06..951d102c1 100644
--- a/src/ace-lib/ace.ml
+++ b/src/ace-lib/ace.ml
@@ -88,7 +88,7 @@ let set_synchronized_status editor status =
 
 let focus { editor } = editor##focus
 
-let create_editor editor_div check_valid_state =
+let create_editor editor_div =
   let editor = edit editor_div in
   Js.Unsafe.set editor "$blockScrolling" (Js.Unsafe.variable "Infinity");
   let data =
@@ -102,8 +102,6 @@ let create_editor editor_div check_valid_state =
   editor##.customData := (data, None);
   editor##setOption (Js.string "displayIndentGuides") (Js.bool false);
   editor##on (Js.string "change") (fun () ->
-      check_valid_state (set_contents data) (fun () -> focus data)
-        (fun () -> set_synchronized_status data true);
       set_synchronized_status data false);
   data
 
diff --git a/src/ace-lib/ace.mli b/src/ace-lib/ace.mli
index 6b922b2c1..32bd13b82 100644
--- a/src/ace-lib/ace.mli
+++ b/src/ace-lib/ace.mli
@@ -17,8 +17,7 @@ type loc = {
   loc_end: int * int;
 }
 
-val create_editor: Dom_html.divElement Js.t
-  -> ((string -> unit) -> (unit -> unit) -> (unit -> unit) -> unit) -> 'a editor
+val create_editor: Dom_html.divElement Js.t -> 'a editor
 
 val is_synchronized : 'a editor -> bool
 
diff --git a/src/ace-lib/ocaml_mode.ml b/src/ace-lib/ocaml_mode.ml
index 46278c8a7..c5bd1fecb 100644
--- a/src/ace-lib/ocaml_mode.ml
+++ b/src/ace-lib/ocaml_mode.ml
@@ -514,8 +514,8 @@ let do_delete ace_editor =
     Ace.remove ace_editor "left"
   end
 
-let create_ocaml_editor div check_valid_state =
-  let ace = Ace.create_editor div check_valid_state in
+let create_ocaml_editor div =
+  let ace = Ace.create_editor div in
   Ace.set_mode ace "ace/mode/ocaml.ocp";
   Ace.set_tab_size ace !config.indent.IndentConfig.i_base;
   let editor = { ace; current_error = None; current_warnings = [] } in
diff --git a/src/ace-lib/ocaml_mode.mli b/src/ace-lib/ocaml_mode.mli
index c86baae05..035058939 100644
--- a/src/ace-lib/ocaml_mode.mli
+++ b/src/ace-lib/ocaml_mode.mli
@@ -24,8 +24,7 @@ type error = msg list
 
 type warning = error
 
-val create_ocaml_editor:
-  Dom_html.divElement Js.t -> ((string -> unit) -> (unit -> unit) -> (unit -> unit) -> unit) -> editor
+val create_ocaml_editor: Dom_html.divElement Js.t -> editor
 val get_editor: editor -> editor Ace.editor
 
 val report_error: editor -> ?set_class: bool -> error option -> warning list -> unit Lwt.t
diff --git a/src/app/learnocaml_common.ml b/src/app/learnocaml_common.ml
index 08a10575a..787753f56 100644
--- a/src/app/learnocaml_common.ml
+++ b/src/app/learnocaml_common.ml
@@ -712,72 +712,11 @@ let mouseover_toggle_signal elt sigvalue setter =
   in
   Manip.Ev.onmouseover elt hdl
 
-(*
-
-   If a user has made no change to a solution for the exercise [id]
-   for 180 seconds, [check_valid_editor_state id] ensures that there is
-   no more recent version of this solution in the server. If this is
-   the case, the user is asked if we should download this solution
-   from the server.
-
-   This function reduces the risk of an involuntary overwriting of a
-   student solution when the solution is open in several clients.
-
-*)
-let is_synchronized_with_server_callback = ref (fun () -> false)
-
-let is_synchronized_with_server () = !is_synchronized_with_server_callback ()
-
-let check_valid_editor_state id =
-  let last_changed = ref (Unix.gettimeofday ()) in
-  fun update_content focus_back on_sync ->
-  let update_local_copy checking_time () =
-    let get_solution () =
-      Learnocaml_local_storage.(retrieve (exercise_state id)).Answer.solution in
-    try let mtime =
-          Learnocaml_local_storage.(retrieve (exercise_state id)).Answer.mtime in
-        if mtime > checking_time then begin
-          let buttons =
-            if is_synchronized_with_server () then
-              [
-                [%i "Fetch from server"],
-                (fun () -> let solution = get_solution () in
-                           Lwt.return (focus_back (); update_content solution; on_sync ()));
-                [%i "Ignore & keep editing"],
-                (fun () -> Lwt.return (focus_back ()));
-              ]
-            else
-              [
-                [%i "Ignore & keep editing"],
-                (fun () -> Lwt.return (focus_back ()));
-                [%i "Fetch from server & overwrite"],
-                (fun () -> let solution = get_solution () in
-                           Lwt.return (focus_back (); update_content solution; on_sync ()));
-              ]
-         in
-         lwt_alert ~title:"Question"
-           ~buttons
-           [ H.p [H.txt [%i "A more recent answer exists on the server. \
-                             Do you want to fetch the new version?"] ] ]
-          end else Lwt.return_unit
-    with
-    | Not_found -> Lwt.return ()
-  in
-  let now = Unix.gettimeofday () in
-  if now -. !last_changed > 180. then (
-    let checking_time = !last_changed in
-    last_changed := now;
-    Lwt.async (update_local_copy checking_time)
-  ) else
-    last_changed := now
-
-
 let ace_display tab =
   let ace = lazy (
     let answer =
       Ocaml_mode.create_ocaml_editor
         (Tyxml_js.To_dom.of_div tab)
-        (fun _ _ _ -> ())
     in
     let ace = Ocaml_mode.get_editor answer in
     Ace.set_font_size ace 16;
@@ -983,12 +922,11 @@ module Editor_button (E : Editor_info) = struct
 
 end
 
-let setup_editor id solution =
+let setup_editor solution =
   let editor_pane = find_component "learnocaml-exo-editor-pane" in
   let editor =
     Ocaml_mode.create_ocaml_editor
       (Tyxml_js.To_dom.of_div editor_pane)
-      (check_valid_editor_state id)
   in
   let ace = Ocaml_mode.get_editor editor in
   Ace.set_contents ace ~reset_undo:true solution;
diff --git a/src/app/learnocaml_common.mli b/src/app/learnocaml_common.mli
index 754d7f4cc..55a08f86f 100644
--- a/src/app/learnocaml_common.mli
+++ b/src/app/learnocaml_common.mli
@@ -218,9 +218,7 @@ module Editor_button (_ : Editor_info) : sig
   val sync : Token.t option Lwt.t -> Learnocaml_data.SMap.key -> (unit -> unit) -> unit
 end
 
-val setup_editor : string -> string -> Ocaml_mode.editor * Ocaml_mode.editor Ace.editor
-
-val is_synchronized_with_server_callback : (unit -> bool) ref
+val setup_editor : string -> Ocaml_mode.editor * Ocaml_mode.editor Ace.editor
 
 val typecheck :
   Learnocaml_toplevel.t ->
diff --git a/src/app/learnocaml_exercise_main.ml b/src/app/learnocaml_exercise_main.ml
index bea8bde16..f9130eef9 100644
--- a/src/app/learnocaml_exercise_main.ml
+++ b/src/app/learnocaml_exercise_main.ml
@@ -179,8 +179,7 @@ let () =
     Tyxml_js.Html5.[ h1 [ txt ex_meta.Exercise.Meta.title ] ;
                      Tyxml_js.Of_dom.of_iFrame text_iframe ] ;
   (* ---- editor pane --------------------------------------------------- *)
-  let editor, ace = setup_editor id solution in
-  is_synchronized_with_server_callback := (fun () -> Ace.is_synchronized ace);
+  let editor, ace = setup_editor solution in
   let module EB = Editor_button (struct let ace = ace let buttons_container = editor_toolbar end) in
   EB.cleanup (Learnocaml_exercise.(access File.template exo));
   EB.sync token id (fun () -> Ace.focus ace; Ace.set_synchronized ace) ;
diff --git a/src/app/learnocaml_playground_main.ml b/src/app/learnocaml_playground_main.ml
index fd12cc7e0..1f53f0695 100644
--- a/src/app/learnocaml_playground_main.ml
+++ b/src/app/learnocaml_playground_main.ml
@@ -64,7 +64,7 @@ let main () =
   (* ---- toplevel pane ------------------------------------------------- *)
   init_toplevel_pane toplevel_launch top toplevel_buttons_group toplevel_button ;
   (* ---- editor pane --------------------------------------------------- *)
-  let editor, ace = setup_editor id solution in
+  let editor, ace = setup_editor solution in
   let module EB = Editor_button (struct let ace = ace let buttons_container = editor_toolbar end) in
   EB.cleanup playground.Playground.template;
   EB.download id;