diff --git a/CHANGES b/CHANGES
index ced2b2b06b..bb80c6f85c 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,6 @@
+===== 10.0 (2022-03-08) =====
+* Make Eliom_state.Ext.discard_state more robust
+
 ===== 9.0 (2021-10-16) =====
 * compatibility with ocsigenserver.5.0.0 (outsourced Ocsipersist)
 
diff --git a/opam b/opam
index b941fc2fca..f37ab24070 100644
--- a/opam
+++ b/opam
@@ -1,6 +1,6 @@
 opam-version: "2.0"
 name: "eliom"
-version: "9.4.0"
+version: "10.0.0"
 maintainer: "dev@ocsigen.org"
 authors: "dev@ocsigen.org"
 synopsis: "Client/server Web framework"
diff --git a/src/lib/eliom_state.server.ml b/src/lib/eliom_state.server.ml
index 1c59c7a768..1b1c2fcba2 100644
--- a/src/lib/eliom_state.server.ml
+++ b/src/lib/eliom_state.server.ml
@@ -1202,20 +1202,23 @@ module Ext = struct
         , Eliom_common.(Hashed_cookies.to_string cookie.sc_hvalue) )
 
   let get_service_cookie_info
+      ?(sitedata =
+        Eliom_request_info.find_sitedata "Eliom_state.get_service_cookie_info")
       ((_, _, cookie) : ([< Eliom_common.cookie_level], [`Service]) state)
     =
     ( cookie
-    , Eliom_common.SessionCookies.find
-        (Eliom_request_info.find_sitedata "Eliom_state.xxx")
-          .Eliom_common.session_services cookie )
+    , Eliom_common.SessionCookies.find sitedata.Eliom_common.session_services
+        cookie )
 
   let get_volatile_data_cookie_info
+      ?(sitedata =
+        Eliom_request_info.find_sitedata
+          "Eliom_state.get_volatile_data_cookie_info")
       ((_, _, cookie) : ([< Eliom_common.cookie_level], [`Data]) state)
     =
     ( cookie
-    , Eliom_common.SessionCookies.find
-        (Eliom_request_info.find_sitedata "Eliom_state.xxx")
-          .Eliom_common.session_data cookie )
+    , Eliom_common.SessionCookies.find sitedata.Eliom_common.session_data cookie
+    )
 
   let get_persistent_cookie_info
       ((_, _, cookie) : ([< Eliom_common.cookie_level], [`Pers]) state)
@@ -1223,12 +1226,11 @@ module Ext = struct
     Eliommod_cookies.Persistent_cookies.Cookies.find cookie >>= fun v ->
     Lwt.return (cookie, v)
 
-  let discard_state ~state =
-    let get_sitedata () =
-      Eliom_request_info.find_sitedata "Eliom_state.discard_state"
-    in
+  let discard_state
+      ?(sitedata = Eliom_request_info.find_sitedata "Eliom_state.discard_state")
+      ~state ()
+    =
     let make_sessgrp n =
-      let sitedata = get_sitedata () in
       sitedata.Eliom_common.site_dir_string, `Session, Left n
     in
     match state with
@@ -1249,7 +1251,6 @@ module Ext = struct
         | None -> ());
         Lwt.return_unit
     | `Session_group _, `Pers, group_name ->
-        let sitedata = get_sitedata () in
         let sgr_o =
           Eliom_common.make_persistent_full_group_name ~cookie_level:`Session
             sitedata.Eliom_common.site_dir_string (Some group_name)
@@ -1257,26 +1258,29 @@ module Ext = struct
         Eliommod_sessiongroups.Pers.remove_group ~cookie_level:`Session sitedata
           sgr_o
     | _, `Service, (_cookie : string) ->
-        let _, {Eliom_common.Service_cookie.session_group_node} =
-          get_service_cookie_info state
+        let () =
+          match get_service_cookie_info ~sitedata state with
+          | exception Not_found -> ()
+          | _, {Eliom_common.Service_cookie.session_group_node} ->
+              Eliommod_sessiongroups.Serv.remove session_group_node
         in
-        Eliommod_sessiongroups.Serv.remove session_group_node;
         Lwt.return_unit
     | _, `Data, _cookie ->
-        let _, {Eliom_common.Data_cookie.session_group_node} =
-          get_volatile_data_cookie_info state
+        let () =
+          match get_volatile_data_cookie_info ~sitedata state with
+          | exception Not_found -> ()
+          | _, {Eliom_common.Data_cookie.session_group_node} ->
+              Eliommod_sessiongroups.Data.remove session_group_node
         in
-        Eliommod_sessiongroups.Data.remove session_group_node;
         Lwt.return_unit
-    | _, `Pers, _cookie ->
-        let%lwt cookie, {Eliommod_cookies.full_state_name; session_group} =
-          get_persistent_cookie_info state
-        in
-        let scope = full_state_name.Eliom_common.user_scope in
-        let sitedata = get_sitedata () in
-        let cookie_level = Eliom_common.cookie_level_of_user_scope scope in
-        Eliommod_sessiongroups.Pers.close_persistent_session2 ~cookie_level
-          sitedata session_group cookie
+    | _, `Pers, _cookie -> (
+        match%lwt get_persistent_cookie_info state with
+        | exception Not_found -> Lwt.return_unit
+        | cookie, {Eliommod_cookies.full_state_name; session_group} ->
+            let scope = full_state_name.Eliom_common.user_scope in
+            let cookie_level = Eliom_common.cookie_level_of_user_scope scope in
+            Eliommod_sessiongroups.Pers.close_persistent_session2 ~cookie_level
+              sitedata session_group cookie)
   (*VVV!!! est-ce que session_group est fullsessgrp ? *)
 
   let fold_sub_states_aux_aux
diff --git a/src/lib/eliom_state.server.mli b/src/lib/eliom_state.server.mli
index c5710e1688..9d9e8cf324 100644
--- a/src/lib/eliom_state.server.mli
+++ b/src/lib/eliom_state.server.mli
@@ -805,8 +805,15 @@ module Ext : sig
     -> ([< Eliom_common.user_level], [< `Service]) state
   (** Same for services *)
 
-  val discard_state : state:('a, 'b) state -> unit Lwt.t
-  (** Discard external states *)
+  val discard_state
+    :  ?sitedata:Eliom_common.sitedata
+    -> state:('a, 'b) state
+    -> unit
+    -> unit Lwt.t
+  (** Discard external states.
+      See {!fold_volatile_sub_states} for explanation about the [?sitedata]
+      parameter.
+  *)
 
   val fold_volatile_sub_states
     :  ?sitedata:Eliom_common.sitedata
@@ -901,13 +908,21 @@ module Ext : sig
   end
 
   val get_service_cookie_info
-    :  ([< Eliom_common.cookie_level], [`Service]) state
+    :  ?sitedata:Eliom_common.sitedata
+    -> ([< Eliom_common.cookie_level], [`Service]) state
     -> service_cookie_info
-  (** Get the infomration about cookies (timeouts, etc.) *)
+  (** Get the infomration about cookies (timeouts, etc.).
+      See {!fold_volatile_sub_states} for explanation about the [?sitedata]
+      parameter.
+  *)
 
   val get_volatile_data_cookie_info
-    :  ([< Eliom_common.cookie_level], [`Data]) state
+    :  ?sitedata:Eliom_common.sitedata
+    -> ([< Eliom_common.cookie_level], [`Data]) state
     -> data_cookie_info
+  (** See {!fold_volatile_sub_states} for explanation about the [?sitedata]
+      parameter.
+  *)
 
   val get_persistent_cookie_info
     :  ([< Eliom_common.cookie_level], [`Pers]) state