diff --git a/passerelle/apps/ovh/migrations/0012_auto_20201027_1121.py b/passerelle/apps/ovh/migrations/0012_auto_20201027_1121.py
new file mode 100644
index 00000000..c9f53457
--- /dev/null
+++ b/passerelle/apps/ovh/migrations/0012_auto_20201027_1121.py
@@ -0,0 +1,25 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.18 on 2020-10-27 10:21
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('ovh', '0011_auto_20201026_1424'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='ovhsmsgateway',
+            name='credit_alert_timestamp',
+            field=models.DateTimeField(editable=False, null=True),
+        ),
+        migrations.AlterField(
+            model_name='ovhsmsgateway',
+            name='username',
+            field=models.CharField(blank=True, help_text='API user created on the SMS account. This field is obsolete once keys and secret fields above are filled.', max_length=64, verbose_name='Username (deprecated)'),
+        ),
+    ]
diff --git a/passerelle/apps/ovh/models.py b/passerelle/apps/ovh/models.py
index 2a07ddd6..e3aeeb24 100644
--- a/passerelle/apps/ovh/models.py
+++ b/passerelle/apps/ovh/models.py
@@ -61,6 +61,7 @@ class OVHSMSGateway(SMSResource):
     username = models.CharField(
         verbose_name=_('Username (deprecated)'),
         max_length=64,
+        blank=True,
         help_text=_('API user created on the SMS account. This field is obsolete once keys and secret '
                     'fields above are filled.'),
     )
@@ -83,7 +84,7 @@ class OVHSMSGateway(SMSResource):
         null=True,
         verbose_name=_('Email addresses to send credit alerts to'),
     )
-    credit_alert_timestamp = models.DateTimeField(null=True)
+    credit_alert_timestamp = models.DateTimeField(null=True, editable=False)
 
     TEST_DEFAULTS = {
         'create_kwargs': {