diff --git a/Gemfile b/Gemfile
index 708603839..b7f37a435 100644
--- a/Gemfile
+++ b/Gemfile
@@ -98,6 +98,7 @@ group :test do
   gem 'capybara-screenshot' # Save a dump of the page when an integration test fails
   gem 'factory_bot'
   gem 'launchy'
+  gem 'rack_session_access'
   gem 'rails-controller-testing'
   gem 'rspec_junit_formatter'
   gem 'selenium-devtools'
diff --git a/Gemfile.lock b/Gemfile.lock
index 14db486bd..872388057 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -513,6 +513,9 @@ GEM
       rack
     rack-test (2.0.2)
       rack (>= 1.3)
+    rack_session_access (0.2.0)
+      builder (>= 2.0.0)
+      rack (>= 1.0.0)
     rails (6.1.7.1)
       actioncable (= 6.1.7.1)
       actionmailbox (= 6.1.7.1)
@@ -887,6 +890,7 @@ DEPENDENCIES
   pundit
   rack-attack
   rack-mini-profiler
+  rack_session_access
   rails
   rails-controller-testing
   rails-erd
diff --git a/config/environments/test.rb b/config/environments/test.rb
index ccaba8feb..4a01914e6 100644
--- a/config/environments/test.rb
+++ b/config/environments/test.rb
@@ -87,4 +87,6 @@ Rails.application.configure do
   silence_warnings do
     BCrypt::Engine::DEFAULT_COST = BCrypt::Engine::MIN_COST
   end
+
+  config.middleware.use RackSessionAccess::Middleware
 end
diff --git a/spec/controllers/users/commencer_controller_spec.rb b/spec/controllers/users/commencer_controller_spec.rb
index 1f4035d9c..8ca93cac3 100644
--- a/spec/controllers/users/commencer_controller_spec.rb
+++ b/spec/controllers/users/commencer_controller_spec.rb
@@ -63,7 +63,7 @@ describe Users::CommencerController, type: :controller do
       end
     end
 
-    context 'when a dossier has been prefilled' do
+    context 'when a dossier has been prefilled by POST before' do
       let(:dossier) { create(:dossier, :brouillon, :prefilled, user: user) }
       let(:path) { dossier.procedure.path }
 
@@ -141,6 +141,85 @@ describe Users::CommencerController, type: :controller do
         end
       end
     end
+
+    context 'when a dossier is being prefilled by GET' do
+      let(:type_de_champ_text) { create(:type_de_champ_text, procedure: published_procedure) }
+      let(:path) { published_procedure.path }
+      let(:user) { create(:user) }
+
+      context "when the dossier does not exists yet" do
+        subject { get :commencer, params: { path: path, "champ_#{type_de_champ_text.to_typed_id}" => "blabla" } }
+
+        shared_examples 'a prefilled brouillon dossier creator' do
+          it 'creates a dossier' do
+            subject
+            expect(Dossier.count).to eq(1)
+            expect(session[:prefill_token]).to eq(Dossier.last.prefill_token)
+            expect(session[:prefill_params]).to eq({ "action" => "commencer", "champ_#{type_de_champ_text.to_typed_id}" => "blabla", "controller" => "users/commencer", "path" => path.to_s })
+            expect(Dossier.last.champs.where(type_de_champ: type_de_champ_text).first.value).to eq("blabla")
+          end
+        end
+
+        context 'when the user is unauthenticated' do
+          it_behaves_like 'a prefilled brouillon dossier creator'
+        end
+
+        context 'when the user is authenticated' do
+          before { sign_in user }
+
+          it_behaves_like 'a prefilled brouillon dossier creator'
+
+          it { expect { subject }.to change { Dossier.last&.user }.from(nil).to(user) }
+
+          it 'sends the notify_new_draft email' do
+            expect { perform_enqueued_jobs { subject } }.to change { ActionMailer::Base.deliveries.count }.by(1)
+
+            dossier = Dossier.last
+            mail = ActionMailer::Base.deliveries.last
+            expect(mail.subject).to eq("Retrouvez votre brouillon pour la démarche « #{dossier.procedure.libelle} »")
+            expect(mail.html_part.body).to include(dossier_path(dossier))
+          end
+        end
+      end
+      context "when prefilled params are passed" do
+        subject { get :commencer, params: { path: path, prefill_token: "token", "champ_#{type_de_champ_text.to_typed_id}" => "blabla" } }
+
+        context "when the associated dossier exists" do
+          let!(:dossier) { create(:dossier, :prefilled, prefill_token: "token") }
+          let!(:champ_text) { create(:champ_text, dossier: dossier, type_de_champ: type_de_champ_text) }
+
+          it "does not create a new dossier" do
+            subject
+            expect(Dossier.count).to eq(1)
+            expect(assigns(:prefilled_dossier)).to eq(dossier)
+          end
+        end
+        context "when the associated dossier does not exists" do
+          it { expect { subject }.to raise_error(ActiveRecord::RecordNotFound) }
+        end
+      end
+      context "when session params exists" do
+        subject { get :commencer, params: { path: path, "champ_#{type_de_champ_text.to_typed_id}" => "blabla" } }
+
+        before do
+          session[:prefill_token] = "token"
+          session[:prefill_params] = { "action" => "commencer", "champ_#{type_de_champ_text.to_typed_id}" => "blabla", "controller" => "users/commencer", "path" => path.to_s }
+        end
+
+        context "when the associated dossier exists" do
+          let!(:dossier) { create(:dossier, :prefilled, prefill_token: "token") }
+
+          it "does not create a new dossier" do
+            subject
+            expect(Dossier.count).to eq(1)
+            expect(assigns(:prefilled_dossier)).to eq(dossier)
+          end
+        end
+        context "when the associated dossier does not exists" do
+          it { expect { subject }.to raise_error(ActiveRecord::RecordNotFound) }
+        end
+      end
+    end
   end
 
   describe '#commencer_test' do
diff --git a/spec/controllers/users/dossiers_controller_spec.rb b/spec/controllers/users/dossiers_controller_spec.rb
index f834508c8..fd100a5fc 100644
--- a/spec/controllers/users/dossiers_controller_spec.rb
+++ b/spec/controllers/users/dossiers_controller_spec.rb
@@ -1066,56 +1066,6 @@ describe Users::DossiersController, type: :controller do
 
             it { is_expected.to redirect_to dossiers_path }
           end
-
-          context 'when prefill values have been stored in session before' do
-            let!(:type_de_champ_1) { create(:type_de_champ_text, procedure: procedure) }
-            let(:value_1) { "any value" }
-
-            let!(:type_de_champ_2) { create(:type_de_champ_textarea, procedure: procedure) }
-            let(:value_2) { "another value" }
-
-            let(:params) {
-              {
-                procedure_id: procedure_id,
-                "champ_#{type_de_champ_1.to_typed_id}" => value_1,
-                "champ_#{type_de_champ_2.to_typed_id}" => value_2
-              }
-            }
-
-            it { expect { subject }.to change { Dossier.count }.by(1) }
-
-            it "prefills the dossier's champs with the given values" do
-              subject
-
-              dossier = Dossier.last
-              expect(find_champ_by_stable_id(dossier, type_de_champ_1.stable_id).value).to eq(value_1)
-              expect(find_champ_by_stable_id(dossier, type_de_champ_2.stable_id).value).to eq(value_2)
-            end
-
-            it { is_expected.to redirect_to siret_dossier_path(id: Dossier.last) }
-
-            context 'when prefill values contain a hash' do
-              let(:value_2) { { evil: "payload" } }
-
-              it "prefills the dossier's champ with the hash stored as a string" do
-                subject
-
-                dossier = Dossier.last
-                expect(find_champ_by_stable_id(dossier, type_de_champ_2.stable_id).value).to eq("{\"evil\"=>\"payload\"}")
-              end
-            end
-
-            context 'when prefill values contain an array' do
-              let(:value_2) { ["a", "b", "c"] }
-
-              it "prefills the dossier's champ with the array stored as a string" do
-                subject
-
-                dossier = Dossier.last
-                expect(find_champ_by_stable_id(dossier, type_de_champ_2.stable_id).value).to eq("[\"a\", \"b\", \"c\"]")
-              end
-            end
-          end
         end
         context 'when user is not logged' do
           it { is_expected.to have_http_status(302) }
diff --git a/spec/rails_helper.rb b/spec/rails_helper.rb
index 340d3d75d..6e1b9fb87 100644
--- a/spec/rails_helper.rb
+++ b/spec/rails_helper.rb
@@ -14,6 +14,7 @@ require 'axe-rspec'
 require 'devise'
 require 'shoulda-matchers'
 require 'view_component/test_helpers'
+require "rack_session_access/capybara"
 
 # Requires supporting ruby files with custom matchers and macros, etc, in
 # spec/support/ and its subdirectories. Files matching `spec/**/*_spec.rb` are
diff --git a/spec/system/users/dossier_prefill_get_spec.rb b/spec/system/users/dossier_prefill_get_spec.rb
index 62aca4e4a..72d212b32 100644
--- a/spec/system/users/dossier_prefill_get_spec.rb
+++ b/spec/system/users/dossier_prefill_get_spec.rb
@@ -31,6 +31,39 @@ describe 'Prefilling a dossier (with a GET request):' do
     end
   end
 
+  context 'when authenticated with existing dossier and session params (ie: reload the page)' do
+    let(:user) { create(:user, password: password) }
+    let(:dossier) { create(:dossier, :prefilled, procedure: procedure, prefill_token: "token", user: nil) }
+
+    before do
+      create(:champ_text, dossier: dossier, type_de_champ: type_de_champ_text, value: text_value)
+
+      page.set_rack_session(prefill_token: "token")
+      page.set_rack_session(prefill_params: { "action" => "commencer", "champ_#{type_de_champ_text.to_typed_id}" => text_value, "controller" => "users/commencer", "path" => procedure.path })
+
+      visit "/users/sign_in"
+      sign_in_with user.email, password
+
+      visit commencer_path(
+        path: procedure.path,
+        "champ_#{type_de_champ_text.to_typed_id}" => text_value
+      )
+
+      click_on "Poursuivre mon dossier prérempli"
+    end
+
+    it "should not create a new dossier" do
+      expect(Dossier.count).to eq(1)
+      expect(dossier.reload.user).to eq(user)
+
+      expect(page).to have_current_path(brouillon_dossier_path(dossier))
+      expect(page).to have_field(type_de_champ_text.libelle, with: text_value)
+
+      expect(page.get_rack_session[:prefill_token]).to be_nil
+      expect(page.get_rack_session[:prefill_params]).to be_nil
+    end
+  end
+
   context 'when unauthenticated' do
     before do
       visit commencer_path(