diff --git a/app/controllers/users/dossiers_controller.rb b/app/controllers/users/dossiers_controller.rb
index fbc164888..55bf11847 100644
--- a/app/controllers/users/dossiers_controller.rb
+++ b/app/controllers/users/dossiers_controller.rb
@@ -9,11 +9,11 @@ module Users
     layout 'procedure_context', only: [:identite, :update_identite, :siret, :update_siret]
 
     ACTIONS_ALLOWED_TO_ANY_USER = [:index, :new, :transferer_all, :deleted_dossiers]
-    ACTIONS_ALLOWED_TO_OWNER_OR_INVITE = [:show, :destroy, :demande, :messagerie, :brouillon, :submit_brouillon, :submit_en_construction, :modifier, :modifier_legacy, :update, :create_commentaire, :papertrail, :restore, :champ]
+    ACTIONS_ALLOWED_TO_OWNER_OR_INVITE = [:show, :destroy, :demande, :messagerie, :brouillon, :submit_brouillon, :submit_en_construction, :modifier, :update, :create_commentaire, :papertrail, :restore, :champ]
 
     before_action :ensure_ownership!, except: ACTIONS_ALLOWED_TO_ANY_USER + ACTIONS_ALLOWED_TO_OWNER_OR_INVITE
     before_action :ensure_ownership_or_invitation!, only: ACTIONS_ALLOWED_TO_OWNER_OR_INVITE
-    before_action :ensure_dossier_can_be_updated, only: [:update_identite, :update_siret, :brouillon, :submit_brouillon, :submit_en_construction, :modifier, :modifier_legacy, :update, :champ]
+    before_action :ensure_dossier_can_be_updated, only: [:update_identite, :update_siret, :brouillon, :submit_brouillon, :submit_en_construction, :modifier, :update, :champ]
     before_action :ensure_dossier_can_be_filled, only: [:brouillon, :modifier, :submit_brouillon, :submit_en_construction, :update]
     before_action :ensure_dossier_can_be_viewed, only: [:show]
     before_action :forbid_invite_submission!, only: [:submit_brouillon]
@@ -263,17 +263,6 @@ module Users
       @dossier = dossier_with_champs
     end
 
-    # Transition to en_construction forks,
-    # so users editing en_construction dossiers won't completely break their changes.
-    # TODO: remove me after fork en_construction feature deploy (PR #8790)
-    def modifier_legacy
-      respond_to do |format|
-        format.turbo_stream do
-          flash.alert = "Une mise à jour de cette page est nécessaire pour poursuivre, veuillez la recharger (touche F5). Attention: le dernier champ modifié n’a pas été sauvegardé, vous devrez le ressaisir."
-        end
-      end
-    end
-
     def submit_en_construction
       @dossier = dossier_with_champs(pj_template: false)
       editing_fork_origin = @dossier.editing_fork_origin
diff --git a/config/routes.rb b/config/routes.rb
index c3dd53caa..88bbb0a8a 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -380,7 +380,6 @@ Rails.application.routes.draw do
         post 'brouillon', to: 'dossiers#submit_brouillon'
         get 'modifier', to: 'dossiers#modifier'
         post 'modifier', to: 'dossiers#submit_en_construction'
-        patch 'modifier', to: 'dossiers#modifier_legacy'
         get 'champs/:stable_id', to: 'dossiers#champ', as: :champ
         get 'merci'
         get 'demande'