diff --git a/Gemfile.lock b/Gemfile.lock
index b74054adf..98b4576bf 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -446,7 +446,7 @@ GEM
     puma (3.12.2)
     pundit (2.0.1)
       activesupport (>= 3.0.0)
-    rack (2.0.7)
+    rack (2.0.8)
     rack-attack (6.0.0)
       rack (>= 1.0, < 3)
     rack-mini-profiler (1.0.1)
diff --git a/app/controllers/instructeurs/dossiers_controller.rb b/app/controllers/instructeurs/dossiers_controller.rb
index e02d91a49..caa08f48a 100644
--- a/app/controllers/instructeurs/dossiers_controller.rb
+++ b/app/controllers/instructeurs/dossiers_controller.rb
@@ -88,33 +88,33 @@ module Instructeurs
     end
 
     def passer_en_instruction
-      if dossier.en_instruction?
-        flash.notice = 'Le dossier est déjà en instruction.'
-      else
+      begin
         dossier.passer_en_instruction!(current_instructeur)
         flash.notice = 'Dossier passé en instruction.'
+      rescue AASM::InvalidTransition => e
+        flash.alert = aasm_error_message(e, target_state: :en_instruction)
       end
 
       render partial: 'state_button_refresh', locals: { dossier: dossier }
     end
 
     def repasser_en_construction
-      if dossier.en_construction?
-        flash.notice = 'Le dossier est déjà en construction.'
-      else
+      begin
         dossier.repasser_en_construction!(current_instructeur)
         flash.notice = 'Dossier repassé en construction.'
+      rescue AASM::InvalidTransition => e
+        flash.alert = aasm_error_message(e, target_state: :en_construction)
       end
 
       render partial: 'state_button_refresh', locals: { dossier: dossier }
     end
 
     def repasser_en_instruction
-      if dossier.en_instruction?
-        flash.notice = 'Le dossier est déjà en instruction.'
-      else
+      begin
         flash.notice = "Le dossier #{dossier.id} a été repassé en instruction."
         dossier.repasser_en_instruction!(current_instructeur)
+      rescue AASM::InvalidTransition => e
+        flash.alert = aasm_error_message(e, target_state: :en_instruction)
       end
 
       render partial: 'state_button_refresh', locals: { dossier: dossier }
@@ -124,20 +124,23 @@ module Instructeurs
       motivation = params[:dossier] && params[:dossier][:motivation]
       justificatif = params[:dossier] && params[:dossier][:justificatif_motivation]
 
-      if dossier.termine?
-        flash.notice = "Le dossier est déjà #{dossier_display_state(dossier, lower: true)}"
-      else
+      begin
         case params[:process_action]
         when "refuser"
+          target_state = :refuse
           dossier.refuser!(current_instructeur, motivation, justificatif)
           flash.notice = "Dossier considéré comme refusé."
         when "classer_sans_suite"
+          target_state = :sans_suite
           dossier.classer_sans_suite!(current_instructeur, motivation, justificatif)
           flash.notice = "Dossier considéré comme sans suite."
         when "accepter"
+          target_state = :accepte
           dossier.accepter!(current_instructeur, motivation, justificatif)
           flash.notice = "Dossier traité avec succès."
         end
+      rescue AASM::InvalidTransition => e
+        flash.alert = aasm_error_message(e, target_state: target_state)
       end
 
       render partial: 'state_button_refresh', locals: { dossier: dossier }
@@ -219,5 +222,13 @@ module Instructeurs
     def mark_annotations_privees_as_read
       current_instructeur.mark_tab_as_seen(dossier, :annotations_privees)
     end
+
+    def aasm_error_message(exception, target_state:)
+      if exception.originating_state == target_state
+        "Le dossier est déjà #{dossier_display_state(target_state, lower: true)}."
+      else
+        "Le dossier est en ce moment #{dossier_display_state(exception.originating_state, lower: true)} : il n’est pas possible de le passer #{dossier_display_state(target_state, lower: true)}."
+      end
+    end
   end
 end
diff --git a/app/helpers/dossier_helper.rb b/app/helpers/dossier_helper.rb
index e279f199b..f4dabce51 100644
--- a/app/helpers/dossier_helper.rb
+++ b/app/helpers/dossier_helper.rb
@@ -47,9 +47,10 @@ module DossierHelper
     dossier.brouillon? && dossier.procedure.close?
   end
 
-  def dossier_display_state(dossier, lower: false)
-    state = I18n.t(dossier.state, scope: [:activerecord, :attributes, :dossier, :state])
-    lower ? state.downcase : state
+  def dossier_display_state(dossier_or_state, lower: false)
+    state = dossier_or_state.is_a?(Dossier) ? dossier_or_state.state : dossier_or_state
+    display_state = I18n.t(state, scope: [:activerecord, :attributes, :dossier, :state])
+    lower ? display_state.downcase : display_state
   end
 
   def dossier_legacy_state(dossier)
diff --git a/app/javascript/new_design/user-sign_up.js b/app/javascript/new_design/user-sign_up.js
index c2a8c4d70..e3c1666b9 100644
--- a/app/javascript/new_design/user-sign_up.js
+++ b/app/javascript/new_design/user-sign_up.js
@@ -13,7 +13,7 @@ delegate('focusout', userNewEmailSelector, () => {
   const suggestedEmailSpan = document.querySelector(emailSuggestionSelector);
 
   const suggestion = suggest(userEmailInput.value);
-  if (suggestion && suggestion.full) {
+  if (suggestion && suggestion.full && suggestedEmailSpan) {
     suggestedEmailSpan.innerHTML = suggestion.full;
     show(document.querySelector(suggestionsSelector));
   } else {
diff --git a/app/views/users/registrations/new.html.haml b/app/views/users/registrations/new.html.haml
index 37bcc2387..7a83cc034 100644
--- a/app/views/users/registrations/new.html.haml
+++ b/app/views/users/registrations/new.html.haml
@@ -8,7 +8,7 @@
     = f.label :email, "Email"
     = f.text_field :email, autofocus: true, placeholder: "Votre adresse email"
 
-    .suspect-email
+    .suspect-email.hidden
       .email-suggestion-title
         Voulez-vous dire
         %span.email-suggestion-address blabla@gmail.com
diff --git a/spec/controllers/instructeurs/dossiers_controller_spec.rb b/spec/controllers/instructeurs/dossiers_controller_spec.rb
index 71e808cb1..db3e30ef0 100644
--- a/spec/controllers/instructeurs/dossiers_controller_spec.rb
+++ b/spec/controllers/instructeurs/dossiers_controller_spec.rb
@@ -112,9 +112,23 @@ describe Instructeurs::DossiersController, type: :controller do
     context 'when the dossier has already been put en_instruction' do
       let(:dossier) { create(:dossier, :en_instruction, procedure: procedure) }
 
-      it 'warns about the error, but doesn’t raise' do
+      it 'warns about the error' do
         expect(dossier.reload.state).to eq(Dossier.states.fetch(:en_instruction))
         expect(response).to have_http_status(:ok)
+        expect(response.body).to have_text('Le dossier est déjà en instruction.')
+      end
+    end
+
+    context 'when the dossier has already been closed' do
+      let(:dossier) { create(:dossier, :accepte, procedure: procedure) }
+
+      it 'doesn’t change the dossier state' do
+        expect(dossier.reload.state).to eq(Dossier.states.fetch(:accepte))
+      end
+
+      it 'warns about the error' do
+        expect(response).to have_http_status(:ok)
+        expect(response.body).to have_text('Le dossier est en ce moment accepté : il n’est pas possible de le passer en instruction.')
       end
     end
   end
@@ -136,9 +150,10 @@ describe Instructeurs::DossiersController, type: :controller do
     context 'when the dossier has already been put en_construction' do
       let(:dossier) { create(:dossier, :en_construction, procedure: procedure) }
 
-      it 'warns about the error, but doesn’t raise' do
+      it 'warns about the error' do
         expect(dossier.reload.state).to eq(Dossier.states.fetch(:en_construction))
         expect(response).to have_http_status(:ok)
+        expect(response.body).to have_text('Le dossier est déjà en construction.')
       end
     end
   end
@@ -161,9 +176,10 @@ describe Instructeurs::DossiersController, type: :controller do
     context 'when the dossier has already been put en_instruction' do
       let(:dossier) { create(:dossier, :en_instruction, procedure: procedure) }
 
-      it 'warns about the error, but doesn’t raise' do
+      it 'warns about the error' do
         expect(dossier.reload.state).to eq(Dossier.states.fetch(:en_instruction))
         expect(response).to have_http_status(:ok)
+        expect(response.body).to have_text('Le dossier est déjà en instruction.')
       end
     end
 
@@ -355,15 +371,18 @@ describe Instructeurs::DossiersController, type: :controller do
     context 'when a dossier is already closed' do
       let(:dossier) { create(:dossier, :accepte, procedure: procedure) }
 
-      before { allow(dossier).to receive(:accepter!) }
+      before { allow(dossier).to receive(:after_accepter) }
 
       subject { post :terminer, params: { process_action: "accepter", procedure_id: procedure.id, dossier_id: dossier.id, dossier: { justificatif_motivation: fake_justificatif } }, format: 'js' }
 
       it 'does not close it again' do
         subject
 
-        expect(dossier).not_to have_received(:accepter!)
+        expect(dossier).not_to have_received(:after_accepter)
+        expect(dossier.state).to eq(Dossier.states.fetch(:accepte))
+
         expect(response).to have_http_status(:ok)
+        expect(response.body).to have_text('Le dossier est déjà accepté.')
       end
     end
   end
diff --git a/spec/helpers/dossier_helper_spec.rb b/spec/helpers/dossier_helper_spec.rb
index e327ca095..2296235f9 100644
--- a/spec/helpers/dossier_helper_spec.rb
+++ b/spec/helpers/dossier_helper_spec.rb
@@ -132,37 +132,20 @@ RSpec.describe DossierHelper, type: :helper do
       expect(subject).to eq('Refusé')
     end
 
-    context "lower: true" do
+    context 'when requesting lowercase' do
       subject { dossier_display_state(dossier, lower: true) }
 
-      it 'brouillon is brouillon' do
+      it 'lowercases the display name' do
         dossier.brouillon!
         expect(subject).to eq('brouillon')
       end
+    end
 
-      it 'en_construction is En construction' do
-        dossier.en_construction!
-        expect(subject).to eq('en construction')
-      end
+    context 'when providing directly a state name' do
+      subject { dossier_display_state(:brouillon) }
 
-      it 'accepte is traité' do
-        dossier.accepte!
-        expect(subject).to eq('accepté')
-      end
-
-      it 'en_instruction is reçu' do
-        dossier.en_instruction!
-        expect(subject).to eq('en instruction')
-      end
-
-      it 'sans_suite is traité' do
-        dossier.sans_suite!
-        expect(subject).to eq('sans suite')
-      end
-
-      it 'refuse is traité' do
-        dossier.refuse!
-        expect(subject).to eq('refusé')
+      it 'generates a display name for the given state' do
+        expect(subject).to eq('Brouillon')
       end
     end
   end