diff --git a/kfet/forms.py b/kfet/forms.py
index 199bac28..09c3a4d0 100644
--- a/kfet/forms.py
+++ b/kfet/forms.py
@@ -134,6 +134,7 @@ class UserRestrictTeamForm(UserForm):
     class Meta(UserForm.Meta):
         fields = ['first_name', 'last_name', 'email']
 
+
 class UserGroupForm(forms.ModelForm):
     groups = forms.ModelMultipleChoiceField(
             Group.objects.filter(name__icontains='K-Fêt'),
@@ -141,16 +142,15 @@ class UserGroupForm(forms.ModelForm):
             required=False)
 
     def clean_groups(self):
-        groups = self.cleaned_data.get('groups')
-        # Si aucun groupe, on le dénomme
-        if not groups:
-            groups = self.instance.groups.exclude(name__icontains='K-Fêt')
-        return groups
+        kfet_groups = self.cleaned_data.get('groups')
+        other_groups = self.instance.groups.exclude(name__icontains='K-Fêt')
+        return list(kfet_groups) + list(other_groups)
 
     class Meta:
-        model  = User
+        model = User
         fields = ['groups']
 
+
 class GroupForm(forms.ModelForm):
     permissions = forms.ModelMultipleChoiceField(
         queryset= Permission.objects.filter(content_type__in=
diff --git a/kfet/tests/test_forms.py b/kfet/tests/test_forms.py
new file mode 100644
index 00000000..7f129a3f
--- /dev/null
+++ b/kfet/tests/test_forms.py
@@ -0,0 +1,56 @@
+# -*- coding: utf-8 -*-
+
+from django.test import TestCase
+from django.contrib.auth.models import User, Group
+
+from kfet.forms import UserGroupForm
+
+
+class UserGroupFormTests(TestCase):
+    """Test suite for UserGroupForm."""
+
+    def setUp(self):
+        # create user
+        self.user = User.objects.create(username="foo", password="foo")
+
+        # create some K-Fêt groups
+        prefix_name = "K-Fêt "
+        names = ["Group 1", "Group 2", "Group 3"]
+        self.kfet_groups = [
+            Group.objects.create(name=prefix_name+name)
+            for name in names
+        ]
+
+        # create a non-K-Fêt group
+        self.other_group = Group.objects.create(name="Other group")
+
+    def test_choices(self):
+        """Only K-Fêt groups are selectable."""
+        form = UserGroupForm(instance=self.user)
+        groups_field = form.fields['groups']
+        self.assertQuerysetEqual(
+            groups_field.queryset,
+            [repr(g) for g in self.kfet_groups],
+            ordered=False,
+        )
+
+    def test_keep_others(self):
+        """User stays in its non-K-Fêt groups."""
+        user = self.user
+
+        # add user to a non-K-Fêt group
+        user.groups.add(self.other_group)
+
+        # add user to some K-Fêt groups through UserGroupForm
+        data = {
+            'groups': [group.pk for group in self.kfet_groups],
+        }
+        form = UserGroupForm(data, instance=user)
+
+        form.is_valid()
+        form.save()
+        self.assertQuerysetEqual(
+            user.groups.all(),
+            [repr(g) for g in [self.other_group] + self.kfet_groups],
+            ordered=False,
+        )