diff --git a/modoboa/admin/models/domain.py b/modoboa/admin/models/domain.py
index 481ca1fe9..76958ec5c 100644
--- a/modoboa/admin/models/domain.py
+++ b/modoboa/admin/models/domain.py
@@ -32,18 +32,10 @@ class Domain(AdminObject):
                             help_text=ugettext_lazy("The domain name"))
     quota = models.PositiveIntegerField(
         default=0,
-        help_text=ugettext_lazy(
-            "Quota shared between mailboxes. Can be expressed in KB, "
-            "MB (default) or GB. A value of 0 means no quota."
-        )
     )
     default_mailbox_quota = models.PositiveIntegerField(
         verbose_name=ugettext_lazy("Default mailbox quota"),
-        default=0,
-        help_text=ugettext_lazy(
-            "Default quota in MB applied to mailboxes. A value of 0 means "
-            "no quota."
-        )
+        default=0
     )
     enabled = models.BooleanField(
         ugettext_lazy("enabled"),
diff --git a/modoboa/admin/serializers.py b/modoboa/admin/serializers.py
index 671b837e9..dfd3ed49b 100644
--- a/modoboa/admin/serializers.py
+++ b/modoboa/admin/serializers.py
@@ -28,8 +28,20 @@ from . import lib, models
 class DomainSerializer(serializers.ModelSerializer):
     """Base Domain serializer."""
 
-    quota = serializers.CharField()
-    default_mailbox_quota = serializers.CharField()
+    quota = serializers.CharField(
+        required=False,
+        help_text=ugettext_lazy(
+            "Quota shared between mailboxes. Can be expressed in KB, "
+            "MB (default) or GB. A value of 0 means no quota."
+        )
+    )
+    default_mailbox_quota = serializers.CharField(
+        required=False,
+        help_text=ugettext_lazy(
+            "Default quota in MB applied to mailboxes. A value of 0 means "
+            "no quota."
+        )
+    )
 
     class Meta:
         model = models.Domain