diff --git a/app/controllers/experts/avis_controller.rb b/app/controllers/experts/avis_controller.rb
index 78de84947..04114174a 100644
--- a/app/controllers/experts/avis_controller.rb
+++ b/app/controllers/experts/avis_controller.rb
@@ -91,7 +91,7 @@ module Experts
         redirect_to url_for(expert_all_avis_path)
       else
         flash[:alert] = user.errors.full_messages
-        redirect_to url_for(sign_up_expert_avis_path(procedure_id, avis_id, email))
+        redirect_to sign_up_expert_avis_path(procedure_id, avis_id, email: email)
       end
     end
 
diff --git a/app/views/avis_mailer/avis_invitation.html.haml b/app/views/avis_mailer/avis_invitation.html.haml
index 52f08054d..319d0aa39 100644
--- a/app/views/avis_mailer/avis_invitation.html.haml
+++ b/app/views/avis_mailer/avis_invitation.html.haml
@@ -1,5 +1,5 @@
 - content_for(:title, 'Invitation à donner votre avis')
-- avis_link = @avis.expert.user.active?.present? ? expert_avis_url(@avis.procedure, @avis) : sign_up_expert_avis_url(@avis.procedure, @avis.id, @avis.expert.email)
+- avis_link = @avis.expert.user.active?.present? ? expert_avis_url(@avis.procedure, @avis) : sign_up_expert_avis_url(@avis.procedure, @avis.id, email: @avis.expert.email)
 
 - content_for(:footer) do
   Merci de ne pas répondre à cet email. Donnez votre avis
diff --git a/app/views/experts/avis/sign_up.html.haml b/app/views/experts/avis/sign_up.html.haml
index f93ed115f..3c4724d0b 100644
--- a/app/views/experts/avis/sign_up.html.haml
+++ b/app/views/experts/avis/sign_up.html.haml
@@ -4,7 +4,7 @@
       %p.description= @dossier.procedure.libelle
       %p.dossier Dossier nº #{@dossier.id}
     .column
-      = form_for(User.new, url: { controller: "experts/avis", action: :update_expert }, method: :post, html: { class: "form" }) do |f|
+      = form_for(User.new, url: sign_up_expert_avis_path(email: @email), method: :post, html: { class: "form" }) do |f|
         %h1 Créez-vous un compte
 
         = f.label :email, "Email"
diff --git a/config/routes.rb b/config/routes.rb
index 4ea2c6ba5..22a203093 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -313,8 +313,13 @@ Rails.application.routes.draw do
             post 'avis' => 'avis#create_avis'
             get 'bilans_bdf'
 
-            get 'sign_up/email/:email' => 'avis#sign_up', constraints: { email: /.*/ }, as: 'sign_up'
-            post 'sign_up/email/:email' => 'avis#update_expert', constraints: { email: /.*/ }
+            get 'sign_up' => 'avis#sign_up'
+            post 'sign_up' => 'avis#update_expert'
+
+            # This redirections are ephemeral, to ensure that emails sent to experts before are still valid
+            # TODO : remove these lines after September, 2021
+            get 'sign_up/email/:email' => 'avis#sign_up', constraints: { email: /.*/ }, as: 'sign_up_legacy'
+            post 'sign_up/email/:email' => 'avis#update_expert', constraints: { email: /.*/ }, as: 'update_expert_legacy'
           end
         end
       end
diff --git a/spec/features/experts/expert_spec.rb b/spec/features/experts/expert_spec.rb
index 6c2f45c05..c2aea0a66 100644
--- a/spec/features/experts/expert_spec.rb
+++ b/spec/features/experts/expert_spec.rb
@@ -12,7 +12,7 @@ feature 'Inviting an expert:' do
 
     context 'when I don’t already have an account' do
       scenario 'I can sign up' do
-        visit sign_up_expert_avis_path(avis.dossier.procedure, avis, avis.expert.email)
+        visit sign_up_expert_avis_path(avis.dossier.procedure, avis, email: avis.expert.email)
 
         expect(page).to have_field('Email', with: avis.expert.email, disabled: true)
         fill_in 'Mot de passe', with: 'This is a very complicated password !'
@@ -29,7 +29,7 @@ feature 'Inviting an expert:' do
         avis.expert.user.reload
       end
       scenario 'I can sign in' do
-        visit sign_up_expert_avis_path(avis.dossier.procedure, avis, avis.expert.email)
+        visit sign_up_expert_avis_path(avis.dossier.procedure, avis, email: avis.expert.email)
 
         expect(page).to have_current_path(new_user_session_path)
         login_as avis.expert.user, scope: :user
diff --git a/spec/features/instructeurs/expert_spec.rb b/spec/features/instructeurs/expert_spec.rb
index 20abe6017..84b3d56a6 100644
--- a/spec/features/instructeurs/expert_spec.rb
+++ b/spec/features/instructeurs/expert_spec.rb
@@ -45,7 +45,7 @@ feature 'Inviting an expert:', js: true do
 
       invitation_email = open_email(expert.email.to_s)
       avis = expert.avis.find_by(dossier: dossier)
-      sign_up_link = sign_up_expert_avis_path(avis.dossier.procedure, avis, avis.expert.email)
+      sign_up_link = sign_up_expert_avis_path(avis.dossier.procedure, avis, email: avis.expert.email)
       expect(invitation_email.body).to include(sign_up_link)
     end
 
diff --git a/spec/mailers/avis_mailer_spec.rb b/spec/mailers/avis_mailer_spec.rb
index 6eac2062f..d9d822d5f 100644
--- a/spec/mailers/avis_mailer_spec.rb
+++ b/spec/mailers/avis_mailer_spec.rb
@@ -14,7 +14,7 @@ RSpec.describe AvisMailer, type: :mailer do
     it { expect(subject.body).to include(instructeur_avis_url(avis.dossier.procedure.id, avis)) }
 
     context 'when the recipient is not already registered' do
-      it { expect(subject.body).to include(sign_up_expert_avis_url(avis.dossier.procedure.id, avis.id, avis.expert.email)) }
+      it { expect(subject.body).to include(sign_up_expert_avis_url(avis.dossier.procedure.id, avis.id, email: avis.expert.email)) }
     end
 
     context 'when the dossier has been deleted before the avis was sent' do