diff --git a/elections/forms.py b/elections/forms.py
index e9da67e..b6bc9fd 100644
--- a/elections/forms.py
+++ b/elections/forms.py
@@ -22,6 +22,15 @@ class ElectionForm(forms.ModelForm):
             self.add_error(
                 "end_date", _("Impossible de terminer l'élection avant de la commencer")
             )
+
+        if self.instance.sent_mail and not cleaned_data["restricted"]:
+            self.add_error(
+                "restricted",
+                _(
+                    "Le mail d'annonce a déjà été envoyé, il n'est pas possible "
+                    "d'ouvrir l'élection à tout le monde"
+                ),
+            )
         return cleaned_data
 
     class Meta:
diff --git a/elections/views.py b/elections/views.py
index a318b03..69a8d74 100644
--- a/elections/views.py
+++ b/elections/views.py
@@ -196,9 +196,22 @@ class ElectionUpdateView(CreatorOnlyEditMixin, SuccessMessageMixin, UpdateView):
     success_message = _("Élection modifiée avec succès !")
     template_name = "elections/election_update.html"
 
+    def get_form(self, form_class=None):
+        form = super().get_form(form_class)
+        if self.object.sent_mail:
+            form.fields["restricted"].disabled = True
+        return form
+
     def get_success_url(self):
         return reverse("election.admin", args=[self.object.pk])
 
+    def form_valid(self, form):
+        # Si on ouvre l'élection à tout le monde, on supprime les votant·e·s
+        # pré-enregistré·e·s
+        if not form.cleaned_data["restricted"]:
+            self.object.registered_voters.all().delete()
+        return super().form_valid(form)
+
 
 class DeleteVoteView(ClosedElectionMixin, FormView):
     model = Election
diff --git a/shared/templates/forms/checkbox.html b/shared/templates/forms/checkbox.html
index 01c54c1..f50ad04 100644
--- a/shared/templates/forms/checkbox.html
+++ b/shared/templates/forms/checkbox.html
@@ -1,6 +1,6 @@
 <div class="control">
   {% if field.auto_id %}
-  <label class="checkbox {% if field.field.required %}{{ form.required_css_class }}{% endif %}">
+  <label class="checkbox {% if field.field.required %}{{ form.required_css_class }}{% endif %}" {% if field.field.disabled %}disabled="" {% endif %}>
     {{ field }} {{ field.label }}
   </label>
   {% endif %}