diff --git a/app/controllers/administrateurs/types_de_champ_controller.rb b/app/controllers/administrateurs/types_de_champ_controller.rb
index 895666182..a771d6231 100644
--- a/app/controllers/administrateurs/types_de_champ_controller.rb
+++ b/app/controllers/administrateurs/types_de_champ_controller.rb
@@ -20,7 +20,12 @@ module Administrateurs
     def update
       type_de_champ = draft.find_and_ensure_exclusive_use(params[:stable_id])
 
-      if type_de_champ.update(type_de_champ_update_params)
+      if type_de_champ.revision_type_de_champ.used_by_routing_rules? && changing_of_type?(type_de_champ)
+        coordinate = draft.coordinate_for(type_de_champ)
+        errors = "« #{type_de_champ.libelle} » est utilisé pour le routage, vous ne pouvez pas modifier son type."
+        @morphed = [champ_component_from(coordinate, focused: false, errors:)]
+        flash.alert = errors
+      elsif type_de_champ.update(type_de_champ_update_params)
         @coordinate = draft.coordinate_for(type_de_champ)
         @morphed = champ_components_starting_at(@coordinate)
 
@@ -86,6 +91,10 @@ module Administrateurs
 
     private
 
+    def changing_of_type?(type_de_champ)
+      type_de_champ_update_params['type_champ'].present? && (type_de_champ_update_params['type_champ'] != type_de_champ.type_champ)
+    end
+
     def champ_components_starting_at(coordinate, offset = 0)
       coordinate
         .siblings_starting_at(offset)
@@ -93,11 +102,12 @@ module Administrateurs
         .map { |c| champ_component_from(c) }
     end
 
-    def champ_component_from(coordinate, focused: false)
+    def champ_component_from(coordinate, focused: false, errors: '')
       TypesDeChampEditor::ChampComponent.new(
-        coordinate: coordinate,
+        coordinate:,
         upper_coordinates: coordinate.upper_siblings,
-        focused: focused
+        focused: focused,
+        errors:
       )
     end
 
diff --git a/spec/controllers/administrateurs/types_de_champ_controller_spec.rb b/spec/controllers/administrateurs/types_de_champ_controller_spec.rb
index 368804097..4b26f71bb 100644
--- a/spec/controllers/administrateurs/types_de_champ_controller_spec.rb
+++ b/spec/controllers/administrateurs/types_de_champ_controller_spec.rb
@@ -3,7 +3,7 @@ describe Administrateurs::TypesDeChampController, type: :controller do
     create(:procedure).tap do |p|
       p.draft_revision.add_type_de_champ(type_champ: :integer_number, libelle: 'l1')
       p.draft_revision.add_type_de_champ(type_champ: :integer_number, libelle: 'l2')
-      p.draft_revision.add_type_de_champ(type_champ: :integer_number, libelle: 'l3')
+      p.draft_revision.add_type_de_champ(type_champ: :drop_down_list, libelle: 'l3')
       p.draft_revision.add_type_de_champ(type_champ: :yes_no, libelle: 'bon dossier', private: true)
     end
   end
@@ -97,6 +97,21 @@ describe Administrateurs::TypesDeChampController, type: :controller do
         expect(flash.alert).to eq(["Le champ « Libelle » doit être rempli"])
       end
     end
+
+    context 'rejected if type changed and routing involved' do
+      let(:params) do
+        default_params.deep_merge(type_de_champ: { type_champ: 'text', stable_id: third_coordinate.stable_id })
+      end
+
+      before do
+        allow_any_instance_of(ProcedureRevisionTypeDeChamp).to receive(:used_by_routing_rules?).and_return(true)
+      end
+
+      it do
+        is_expected.to have_http_status(:ok)
+        expect(flash.alert).to include("utilisé pour le routage")
+      end
+    end
   end
 
   # l1, l2, l3 => l1, l3, l2