diff --git a/modoboa/admin/api/v1/serializers.py b/modoboa/admin/api/v1/serializers.py
index b1769ccc8..0ba2c6b3c 100644
--- a/modoboa/admin/api/v1/serializers.py
+++ b/modoboa/admin/api/v1/serializers.py
@@ -471,8 +471,10 @@ class AliasSerializer(serializers.ModelSerializer):
         try:
             local_part, self.domain = admin_models.validate_alias_address(
                 value, self.context["request"].user, instance=self.instance)
-        except (AliasExists, ValidationError) as err:
+        except ValidationError as err:
             raise serializers.ValidationError(err)
+        except AliasExists:
+            raise serializers.ValidationError(_("This alias already exists"))
         return value.lower()
 
     def create(self, validated_data):
diff --git a/modoboa/admin/api/v2/tests.py b/modoboa/admin/api/v2/tests.py
index 0f09ae935..db5881cbb 100644
--- a/modoboa/admin/api/v2/tests.py
+++ b/modoboa/admin/api/v2/tests.py
@@ -535,7 +535,7 @@ class AliasViewSetTestCase(ModoAPITestCase):
 
         data = {"address": "alias@test.com"}
         resp = self.client.post(url, data, format="json")
-        self.assertEqual(resp.status_code, 409)
+        self.assertEqual(resp.status_code, 400)
 
         al_id = models.Alias.objects.get(address="alias@test.com").pk
         self.assertEqual(resp.json()["id"], al_id)