diff --git a/src/widgets/ot_calendar.eliom b/src/widgets/ot_calendar.eliom
index 4f0efde3..9841913e 100644
--- a/src/widgets/ot_calendar.eliom
+++ b/src/widgets/ot_calendar.eliom
@@ -561,10 +561,10 @@ let make :
 
 let%server make :
    ?init:int * int * int
-  -> ?highlight:(int -> int -> int list Lwt.t) Eliom_client_value.t
+  -> ?highlight:(int -> int -> int list) Eliom_client_value.t
   -> ?click_non_highlighted:bool
   -> ?update:(int * int * int) React.E.t Eliom_client_value.t
-  -> ?action:(int -> int -> int -> unit Lwt.t) Eliom_client_value.t
+  -> ?action:(int -> int -> int -> unit) Eliom_client_value.t
   -> ?period:
        CalendarLib.Date.field CalendarLib.Date.date
        * CalendarLib.Date.field CalendarLib.Date.date
diff --git a/src/widgets/ot_calendar.eliomi b/src/widgets/ot_calendar.eliomi
index 6e72fd32..2f56cc5f 100644
--- a/src/widgets/ot_calendar.eliomi
+++ b/src/widgets/ot_calendar.eliomi
@@ -41,10 +41,10 @@ type button_labels =
 
 val make :
    ?init:int * int * int
-  -> ?highlight:(int -> int -> int list Lwt.t) Eliom_client_value.t
+  -> ?highlight:(int -> int -> int list) Eliom_client_value.t
   -> ?click_non_highlighted:bool
   -> ?update:(int * int * int) React.E.t Eliom_client_value.t
-  -> ?action:(int -> int -> int -> unit Lwt.t) Eliom_client_value.t
+  -> ?action:(int -> int -> int -> unit) Eliom_client_value.t
   -> ?period:
        CalendarLib.Date.field CalendarLib.Date.date
        * CalendarLib.Date.field CalendarLib.Date.date
diff --git a/src/widgets/ot_carousel.eliom b/src/widgets/ot_carousel.eliom
index fd76dc66..a2f94202 100644
--- a/src/widgets/ot_carousel.eliom
+++ b/src/widgets/ot_carousel.eliom
@@ -1,3 +1,5 @@
+open Eio.Std
+
 (* Ocsigen
  * http://www.ocsigen.org
  *
@@ -39,7 +41,7 @@ open%client Js_of_ocaml
 [%%client open Js_of_ocaml_lwt]
 [%%shared open Eliom_content.Html]
 [%%shared open Eliom_content.Html.F]
-[%%shared open Lwt.Syntax]
+[%%shared]
 
 let%client clX = Ot_swipe.clX
 let%client clY = Ot_swipe.clY
@@ -587,9 +589,7 @@ let%client set_default_fail f =
       :> exn -> Html_types.div_content Eliom_content.Html.elt)
 
 let%shared generate_content generator =
-  Lwt.catch
-    (fun () -> Eliom_shared.Value.local generator ())
-    (fun e -> Lwt.return (default_fail e))
+  try Eliom_shared.Value.local generator () with e -> default_fail e
 
 (* on the client side we generate the contents of the initially visible page
    asynchronously so the tabs will be rendered right away *)
@@ -606,8 +606,8 @@ let%client generate_initial_contents ~spinner sleeper gen =
 
 (* on the server side we generate all the visible contents right away *)
 let%server generate_initial_contents ~spinner:_ _ gen =
-  let* contents = generate_content gen in
-  Lwt.return (contents, ref @@ None)
+  let contents = generate_content gen in
+  contents, ref @@ None
 
 let%shared
     make_lazy
@@ -628,30 +628,30 @@ let%shared
   =
   let gen_contents =
     (gen_contents
-      :> (unit -> Html_types.div_content elt Lwt.t) Eliom_shared.Value.t list)
+      :> (unit -> Html_types.div_content elt) Eliom_shared.Value.t list)
+  in
+  let sleeper, wakener =
+    Promise.create
+      (* TODO: ciao-lwt: Translation is incomplete, [Promise.await] must be called on the promise when it's part of control-flow. *)
+      ()
   in
-  let sleeper, wakener = Lwt.wait () in
-  let mk_contents : int -> 'gen -> ('a elt * ('a elt * 'gen) option ref) Lwt.t =
+  let mk_contents : int -> 'gen -> 'a elt * ('a elt * 'gen) option ref =
    fun i gen ->
     if i = position
     then generate_initial_contents ~spinner sleeper gen
     else
-      Lwt.return
-      @@
       let s = spinner () in
       s, ref @@ Some (s, gen)
   in
-  let* contents, spinners_and_generators =
-    Lwt.map List.split
-    @@ Lwt_list.map_s (fun x -> x)
-    @@ List.mapi mk_contents gen_contents
+  let contents, spinners_and_generators =
+    List.split (List.map (fun x -> x) (List.mapi mk_contents gen_contents))
   in
   let carousel =
     make ?a ?vertical ~position ?transition_duration ?inertia ?swipeable
       ?allow_overswipe ?update ?disabled ?full_height ?make_transform
       ?make_page_attribute contents
   in
-  Lwt.wakeup wakener carousel.elt;
+  Promise.resolve wakener carousel.elt;
   (* generate initial content (client-side) *)
   (* replace spinners with content when switched to for the first time *)
   let _ =
@@ -677,7 +677,7 @@ let%shared
                 | None -> Lwt.return ())
        : unit)]
   in
-  Lwt.return carousel
+  carousel
 
 let%shared bullet_class i pos size =
   Eliom_shared.React.S.l2
diff --git a/src/widgets/ot_carousel.eliomi b/src/widgets/ot_carousel.eliomi
index d2424bf7..0bd09c1a 100644
--- a/src/widgets/ot_carousel.eliomi
+++ b/src/widgets/ot_carousel.eliomi
@@ -148,10 +148,10 @@ val make_lazy :
         -> Html_types.div_attrib Eliom_content.Html.D.attrib list)
          Eliom_shared.Value.t
   -> ?spinner:(unit -> Html_types.div_content Eliom_content.Html.elt)
-  -> (unit -> [< Html_types.div_content] Eliom_content.Html.elt Lwt.t)
+  -> (unit -> [< Html_types.div_content] Eliom_content.Html.elt)
        Eliom_shared.Value.t
        list
-  -> [> `Div] t Lwt.t
+  -> [> `Div] t
 (** same as [make] except for the last argument. Instead of supplying the
     contents for each page directly, supply a for each page a shared content
     generator function. Contents will be generated and filled lazily, i.e. when
diff --git a/src/widgets/ot_drawer.eliom b/src/widgets/ot_drawer.eliom
index 6703b24e..65644e41 100644
--- a/src/widgets/ot_drawer.eliom
+++ b/src/widgets/ot_drawer.eliom
@@ -1,3 +1,5 @@
+open Eio.Std
+
 [%%shared
 (* Ocsigen
  * http://www.ocsigen.org
@@ -113,11 +115,11 @@ let%shared
     D.div ~a:(a_class ("ot-drawer-bckgrnd" :: bckgrnd_init_class) :: a) [d]
   in
   let bind_touch :
-    ((unit -> unit) Lwt.t * (unit -> unit) Lwt.u) Eliom_client_value.t
+    ((unit -> unit) Promise.t * (unit -> unit) Lwt.u) Eliom_client_value.t
     =
     [%client Lwt.wait ()]
   in
-  let touch_thread = [%client (ref Lwt.return_unit : unit Lwt.t ref)] in
+  let touch_thread = [%client (ref Lwt.return_unit : unit Promise.t ref)] in
   let reset_scroll_pos =
     [%client
       (fun () ->
@@ -179,7 +181,7 @@ let%shared
          html_ManipClass_remove "ot-drawer-open";
          html_ManipClass_remove "ot-drawer-closing");
        Lwt.return_unit
-       : unit Lwt.t)]
+       : unit Promise.t)]
   in
   let _ =
     [%client
diff --git a/src/widgets/ot_picture_uploader.eliom b/src/widgets/ot_picture_uploader.eliom
index 9d31d45d..5527d6d3 100644
--- a/src/widgets/ot_picture_uploader.eliom
+++ b/src/widgets/ot_picture_uploader.eliom
@@ -446,10 +446,7 @@ let%client bind_input input preview ?container ?reset () =
 type cropping = (float * float * float * float) React.S.t
 
 type 'a upload =
-  ?progress:(int -> int -> unit)
-  -> ?cropping:cropping
-  -> File.file Js.t
-  -> 'a Lwt.t]
+  ?progress:(int -> int -> unit) -> ?cropping:cropping -> File.file Js.t -> 'a]
 
 let%client ocaml_service_upload ~service ~arg ?progress ?cropping file =
   Eliom_client.call_ocaml_service ~service () ?upload_progress:progress
@@ -499,7 +496,7 @@ let%server mk_service name arg_deriver =
 
 let%shared
     mk_form
-      ?(after_submit = fun () -> Lwt.return_unit)
+      ?(after_submit = fun () -> ())
       ?crop
       ?input:(input_a, input_content = [], [])
       ?submit:(submit_a, submit_content = [], [])
@@ -532,4 +529,4 @@ let%shared
          ~upload:~%upload ~after_submit:~%after_submit ()
        : unit)]
   in
-  Lwt.return form
+  form
diff --git a/src/widgets/ot_picture_uploader.eliomi b/src/widgets/ot_picture_uploader.eliomi
index df129b10..a3c0a3c7 100644
--- a/src/widgets/ot_picture_uploader.eliomi
+++ b/src/widgets/ot_picture_uploader.eliomi
@@ -33,10 +33,7 @@ open Js_of_ocaml
 type cropping = (float * float * float * float) React.S.t
 
 type 'a upload =
-  ?progress:(int -> int -> unit)
-  -> ?cropping:cropping
-  -> File.file Js.t
-  -> 'a Lwt.t
+  ?progress:(int -> int -> unit) -> ?cropping:cropping -> File.file Js.t -> 'a
 
 type ('a, 'b) service =
   ( unit
@@ -142,7 +139,7 @@ val submit :
 (** Create a button with [ot-pup-sumit] clas *)
 
 val mk_form :
-   ?after_submit:(unit -> unit Lwt.t)
+   ?after_submit:(unit -> unit)
   -> ?crop:float option
   -> ?input:
        [< Html_types.label_attrib > `Class] Eliom_content.Html.attrib list
@@ -151,7 +148,7 @@ val mk_form :
        [< Html_types.button_attrib > `Class] Eliom_content.Html.attrib list
        * [< Html_types.button_content_fun] Eliom_content.Html.elt list
   -> 'a upload
-  -> [> `Form] Eliom_content.Html.elt Lwt.t
+  -> [> `Form] Eliom_content.Html.elt
 (** Ready-to-use form. Customizable with
     [input], the input button content, [submit], the submit button content.
     If [crop] is present, cropping is enable, with the optional ratio it is.
diff --git a/src/widgets/ot_pulltorefresh.eliom b/src/widgets/ot_pulltorefresh.eliom
index 23aaf803..16389ac9 100644
--- a/src/widgets/ot_pulltorefresh.eliom
+++ b/src/widgets/ot_pulltorefresh.eliom
@@ -175,7 +175,7 @@ let make
       ?(refresh_timeout = 20.)
       ?(header = [%shared default_header])
       ~content
-      (afterPull : (unit -> bool Lwt.t) Eliom_client_value.t)
+      (afterPull : (unit -> bool) Eliom_client_value.t)
   =
   if app_only && not (Eliom_client.is_client_app ())
   then div ~a [content]
diff --git a/src/widgets/ot_pulltorefresh.eliomi b/src/widgets/ot_pulltorefresh.eliomi
index c45d0054..fb64e4bf 100644
--- a/src/widgets/ot_pulltorefresh.eliomi
+++ b/src/widgets/ot_pulltorefresh.eliomi
@@ -25,7 +25,7 @@ val make :
              list)
          Eliom_shared.Value.t
   -> content:'a Eliom_content.Html.elt
-  -> (unit -> bool Lwt.t) Eliom_client_value.t
+  -> (unit -> bool) Eliom_client_value.t
   -> 'a Eliom_content.Html.elt
 (**
    Creates a pull-to-refresh container from an html element.
diff --git a/src/widgets/ot_spinner.eliom b/src/widgets/ot_spinner.eliom
index 6a13f3fc..a58d423c 100644
--- a/src/widgets/ot_spinner.eliom
+++ b/src/widgets/ot_spinner.eliom
@@ -22,7 +22,7 @@
 open%client Js_of_ocaml
 
 [%%shared open Eliom_content.Html]
-[%%shared open Lwt.Syntax]
+[%%shared]
 [%%shared open Eliom_content.Html.F]
 [%%client open Eliom_shared]
 
@@ -58,20 +58,19 @@ let%server with_spinner ?(a = []) ?spinner:_ ?fail thread =
   let a = (a :> Html_types.div_attrib attrib list) in
   let fail =
     ((match fail with
-     | Some fail -> (fail :> exn -> Html_types.div_content elt list Lwt.t)
-     | None -> fun e -> Lwt.return (default_fail e))
-      :> exn -> Html_types.div_content elt list Lwt.t)
+     | Some fail -> (fail :> exn -> Html_types.div_content elt list)
+     | None -> fun e -> default_fail e)
+      :> exn -> Html_types.div_content elt list)
   in
-  let* v =
-    Lwt.catch
-      (fun () ->
-         let* v = thread in
-         Lwt.return (v :> Html_types.div_content_fun F.elt list))
-      (fun e ->
-         let* v = fail e in
-         Lwt.return (v :> Html_types.div_content_fun F.elt list))
+  let v =
+    try
+      let v = thread in
+      (v :> Html_types.div_content_fun F.elt list)
+    with e ->
+      let v = fail e in
+      (v :> Html_types.div_content_fun F.elt list)
   in
-  Lwt.return (D.div ~a:(a_class ["ot-spinner"] :: a) v)
+  D.div ~a:(a_class ["ot-spinner"] :: a) v
 
 [%%client
 let num_active_spinners, set_num_active_spinners = React.S.create 0
diff --git a/src/widgets/ot_spinner.eliomi b/src/widgets/ot_spinner.eliomi
index c8fb10da..861b5fcd 100644
--- a/src/widgets/ot_spinner.eliomi
+++ b/src/widgets/ot_spinner.eliomi
@@ -1,3 +1,5 @@
+open Eio.Std
+
 (* Ocsigen Toolkit
  * http://www.ocsigen.org/ocsigen-toolkit
  *
@@ -26,9 +28,9 @@
 val with_spinner :
    ?a:[< Html_types.div_attrib] Eliom_content.Html.attrib list
   -> ?spinner:[< Html_types.div_content] Eliom_content.Html.elt list
-  -> ?fail:(exn -> [< Html_types.div_content] Eliom_content.Html.elt list Lwt.t)
-  -> [< Html_types.div_content] Eliom_content.Html.elt list Lwt.t
-  -> [> `Div] Eliom_content.Html.elt Lwt.t
+  -> ?fail:(exn -> [< Html_types.div_content] Eliom_content.Html.elt list)
+  -> [< Html_types.div_content] Eliom_content.Html.elt list Promise.t
+  -> [> `Div] Eliom_content.Html.elt
 (** On client side, [with_spinner th] returns immediately a spinner
     while Lwt thread [th] is not finished, that will automatically
     be replaced by the result of [th] when finished.
diff --git a/src/widgets/ot_time_picker.eliom b/src/widgets/ot_time_picker.eliom
index a7f3f25f..151595db 100644
--- a/src/widgets/ot_time_picker.eliom
+++ b/src/widgets/ot_time_picker.eliom
@@ -381,7 +381,7 @@ let display_hours_minutes_seq ?h24 f =
   Eliom_shared.React.S.l2 [%shared display_hours_minutes_seq ?h24:~%h24 ~%f]
 
 let show_minutes_aux
-      ?(action : (int * int -> unit Lwt.t) Eliom_client_value.t option)
+      ?(action : (int * int -> unit) Eliom_client_value.t option)
       e_m
       hm
       f_e_m
@@ -407,7 +407,7 @@ let get_angle_signal ?round =
         | _, _ -> e]
 
 let make_hours_minutes_seq_24h
-      ?(action : (int * int -> unit Lwt.t) Eliom_client_value.t option)
+      ?(action : (int * int -> unit) Eliom_client_value.t option)
       ?(init = 0, 0)
       ?(update : (int * int) React.E.t Eliom_client_value.t option)
       ?round_5
diff --git a/src/widgets/ot_time_picker.eliomi b/src/widgets/ot_time_picker.eliomi
index 09c56569..f7bfb804 100644
--- a/src/widgets/ot_time_picker.eliomi
+++ b/src/widgets/ot_time_picker.eliomi
@@ -23,7 +23,7 @@
 (** This module implements a clock-style time picker. *)
 
 val make :
-   ?action:(int * int -> unit Lwt.t) Eliom_client_value.t
+   ?action:(int * int -> unit) Eliom_client_value.t
   -> ?init:int * int
   -> ?update:(int * int) React.E.t Eliom_client_value.t
   -> ?round_5:bool
@@ -56,7 +56,7 @@ val make :
     is a function that can be called to go back to hours selection. *)
 
 val make_hours_minutes_seq :
-   ?action:(int * int -> unit Lwt.t) Eliom_client_value.t
+   ?action:(int * int -> unit) Eliom_client_value.t
   -> ?init:int * int
   -> ?update:(int * int) React.E.t Eliom_client_value.t
   -> ?round_5:bool