diff --git a/orchestra/contrib/accounts/actions.py b/orchestra/contrib/accounts/actions.py
index 1712da8a..da58022c 100644
--- a/orchestra/contrib/accounts/actions.py
+++ b/orchestra/contrib/accounts/actions.py
@@ -175,7 +175,7 @@ def delete_related_services(modeladmin, request, queryset):
     for model, objs in collector.model_objs.items():
         count = 0
         # discount main systemuser
-        if model is modeladmin.model.main_systemuser.field.rel.to:
+        if model is modeladmin.model.main_systemuser.field.model:
             count = len(objs) - 1
         # Discount account
         elif model is not modeladmin.model and model in registered_services:
diff --git a/orchestra/contrib/accounts/forms.py b/orchestra/contrib/accounts/forms.py
index 4a7dcc6b..c3e308b1 100644
--- a/orchestra/contrib/accounts/forms.py
+++ b/orchestra/contrib/accounts/forms.py
@@ -34,7 +34,7 @@ def create_account_creation_form():
             fields[field_name] = forms.BooleanField(
                 initial=True, required=False, label=label, help_text=help_text)
             create_related.append((model, key, kwargs, help_text))
-        
+
     def clean(self, create_related=create_related):
         """ unique usernames between accounts and system users """
         cleaned_data = UserCreationForm.clean(self)
@@ -47,7 +47,7 @@ def create_account_creation_form():
             # Previous validation error
             return
         errors = {}
-        systemuser_model = Account.main_systemuser.field.rel.to
+        systemuser_model = Account.main_systemuser.field.model
         if systemuser_model.objects.filter(username=account.username).exists():
             errors['username'] = _("A system user with this name already exists.")
         for model, key, related_kwargs, __ in create_related:
@@ -62,11 +62,11 @@ def create_account_creation_form():
                     params={'type': verbose_name})
         if errors:
             raise ValidationError(errors)
-    
+
     def save_model(self, account):
         enable_systemuser=self.cleaned_data['enable_systemuser']
         account.save(active_systemuser=enable_systemuser)
-    
+
     def save_related(self, account):
         for model, key, related_kwargs, __ in settings.ACCOUNTS_CREATE_RELATED:
             model = apps.get_model(model)
@@ -76,14 +76,14 @@ def create_account_creation_form():
                     key: eval(value, {'account': account}) for key, value in related_kwargs.items()
                 }
                 model.objects.create(account=account, **kwargs)
-    
+
     fields.update({
         'create_related_fields': list(fields.keys()),
         'clean': clean,
         'save_model': save_model,
         'save_related': save_related,
     })
-    
+
     return type('AccountCreationForm', (UserCreationForm,), fields)
 
 
diff --git a/orchestra/contrib/bills/helpers.py b/orchestra/contrib/bills/helpers.py
index 7efbd610..e5986b5c 100644
--- a/orchestra/contrib/bills/helpers.py
+++ b/orchestra/contrib/bills/helpers.py
@@ -21,7 +21,7 @@ def validate_contact(request, bill, error=True):
         message = msg.format(relation=_("Related"), account=account, url=url)
         send(request, mark_safe(message))
         valid = False
-    main = type(bill).account.field.rel.to.objects.get_main()
+    main = type(bill).account.field.model.objects.get_main()
     if not hasattr(main, 'billcontact'):
         account = force_text(main)
         url = reverse('admin:accounts_account_change', args=(main.id,))
diff --git a/orchestra/contrib/lists/serializers.py b/orchestra/contrib/lists/serializers.py
index c40dc010..c4a666fd 100644
--- a/orchestra/contrib/lists/serializers.py
+++ b/orchestra/contrib/lists/serializers.py
@@ -12,7 +12,7 @@ from .models import List
 
 class RelatedDomainSerializer(AccountSerializerMixin, RelatedHyperlinkedModelSerializer):
     class Meta:
-        model = List.address_domain.field.rel.to
+        model = List.address_domain.field.model
         fields = ('url', 'id', 'name')
 
 
@@ -26,14 +26,14 @@ class ListSerializer(AccountSerializerMixin, SetPasswordHyperlinkedSerializer):
                              'This value may contain any ascii character except for '
                              ' \'/"/\\/ characters.'), 'invalid'),
         ])
-    
+
     address_domain = RelatedDomainSerializer(required=False)
-    
+
     class Meta:
         model = List
         fields = ('url', 'id', 'name', 'password', 'address_name', 'address_domain', 'admin_email', 'is_active',)
         postonly_fields = ('name', 'password')
-    
+
     def validate_address_domain(self, address_name):
         if self.instance:
             address_domain = address_domain or self.instance.address_domain
diff --git a/orchestra/contrib/mailboxes/models.py b/orchestra/contrib/mailboxes/models.py
index ee4c3594..8581d0ec 100644
--- a/orchestra/contrib/mailboxes/models.py
+++ b/orchestra/contrib/mailboxes/models.py
@@ -44,7 +44,7 @@ class Mailbox(models.Model):
     def active(self):
         try:
             return self.is_active and self.account.is_active
-        except type(self).account.field.rel.to.DoesNotExist:
+        except type(self).account.field.model.DoesNotExist:
             return self.is_active
 
     def disable(self):
diff --git a/orchestra/contrib/mailboxes/serializers.py b/orchestra/contrib/mailboxes/serializers.py
index 18bc09ce..264afac8 100644
--- a/orchestra/contrib/mailboxes/serializers.py
+++ b/orchestra/contrib/mailboxes/serializers.py
@@ -8,17 +8,17 @@ from .models import Mailbox, Address
 
 class RelatedDomainSerializer(AccountSerializerMixin, RelatedHyperlinkedModelSerializer):
     class Meta:
-        model = Address.domain.field.rel.to
+        model = Address.domain.field.model
         fields = ('url', 'id', 'name')
 
 
 class RelatedAddressSerializer(AccountSerializerMixin, serializers.HyperlinkedModelSerializer):
     domain = RelatedDomainSerializer()
-    
+
     class Meta:
         model = Address
         fields = ('url', 'id', 'name', 'domain', 'forward')
-#    
+#
 #    def from_native(self, data, files=None):
 #        queryset = self.opts.model.objects.filter(account=self.account)
 #        return get_object_or_404(queryset, name=data['name'])
@@ -26,7 +26,7 @@ class RelatedAddressSerializer(AccountSerializerMixin, serializers.HyperlinkedMo
 
 class MailboxSerializer(AccountSerializerMixin, SetPasswordHyperlinkedSerializer):
     addresses = RelatedAddressSerializer(many=True, read_only=True)
-    
+
     class Meta:
         model = Mailbox
         fields = (
@@ -44,11 +44,11 @@ class RelatedMailboxSerializer(AccountSerializerMixin, RelatedHyperlinkedModelSe
 class AddressSerializer(AccountSerializerMixin, serializers.HyperlinkedModelSerializer):
     domain = RelatedDomainSerializer()
     mailboxes = RelatedMailboxSerializer(many=True, required=False) #allow_add_remove=True
-    
+
     class Meta:
         model = Address
         fields = ('url', 'id', 'name', 'domain', 'mailboxes', 'forward')
-    
+
     def validate(self, attrs):
         attrs = super(AddressSerializer, self).validate(attrs)
         if not attrs['mailboxes'] and not attrs['forward']:
diff --git a/orchestra/contrib/orders/signals.py b/orchestra/contrib/orders/signals.py
index 5ddc818f..c1b541e8 100644
--- a/orchestra/contrib/orders/signals.py
+++ b/orchestra/contrib/orders/signals.py
@@ -15,7 +15,7 @@ def cancel_orders(sender, **kwargs):
     if sender._meta.app_label not in settings.ORDERS_EXCLUDED_APPS:
         instance = kwargs['instance']
         # Account delete will delete all related orders, no need to maintain order consistency
-        if isinstance(instance, Order.account.field.rel.to):
+        if isinstance(instance, Order.account.field.model):
             return
         if type(instance) in services:
             for order in Order.objects.by_object(instance).active():
diff --git a/orchestra/contrib/saas/services/helpers.py b/orchestra/contrib/saas/services/helpers.py
index bf081995..7418bc9d 100644
--- a/orchestra/contrib/saas/services/helpers.py
+++ b/orchestra/contrib/saas/services/helpers.py
@@ -42,7 +42,7 @@ def clean_custom_url(saas):
         )
     except Website.DoesNotExist:
         # get or create domain
-        Domain = Website.domains.field.rel.to
+        Domain = Website.domains.field.model
         try:
             domain = Domain.objects.get(name=url.netloc)
         except Domain.DoesNotExist:
@@ -51,7 +51,7 @@ def clean_custom_url(saas):
             })
         if domain.account != account:
             raise ValidationError({
-                'custom_url': _("Domain %s does not belong to account %s, it's from %s.") % 
+                'custom_url': _("Domain %s does not belong to account %s, it's from %s.") %
                     (url.netloc, account, domain.account),
             })
         # Create new website for custom_url
@@ -110,7 +110,7 @@ def create_or_update_directive(saas):
             account=account,
         )
     except Website.DoesNotExist:
-        Domain = Website.domains.field.rel.to
+        Domain = Website.domains.field.model
         domain = Domain.objects.get(name=url.netloc)
         # Create new website for custom_url
         tgt_server = Server.objects.get(name='web.pangea.lan')
diff --git a/orchestra/contrib/systemusers/models.py b/orchestra/contrib/systemusers/models.py
index c7e9abd0..92576646 100644
--- a/orchestra/contrib/systemusers/models.py
+++ b/orchestra/contrib/systemusers/models.py
@@ -61,7 +61,7 @@ class SystemUser(models.Model):
     def active(self):
         try:
             return self.is_active and self.account.is_active
-        except type(self).account.field.rel.to.DoesNotExist:
+        except type(self).account.field.model.DoesNotExist:
             return self.is_active
 
     @cached_property
diff --git a/orchestra/contrib/websites/serializers.py b/orchestra/contrib/websites/serializers.py
index 89fd6ce8..f38203a3 100644
--- a/orchestra/contrib/websites/serializers.py
+++ b/orchestra/contrib/websites/serializers.py
@@ -13,23 +13,23 @@ from .validators import validate_domain_protocol
 
 class RelatedDomainSerializer(AccountSerializerMixin, RelatedHyperlinkedModelSerializer):
     class Meta:
-        model = Website.domains.field.rel.to
+        model = Website.domains.field.model
         fields = ('url', 'id', 'name')
 
 
 class RelatedWebAppSerializer(AccountSerializerMixin, RelatedHyperlinkedModelSerializer):
     class Meta:
-        model = Content.webapp.field.rel.to
+        model = Content.webapp.field.model
         fields = ('url', 'id', 'name', 'type')
 
 
 class ContentSerializer(serializers.ModelSerializer):
     webapp = RelatedWebAppSerializer()
-    
+
     class Meta:
         model = Content
         fields = ('webapp', 'path')
-    
+
     def get_identity(self, data):
         return '%s-%s' % (data.get('website'), data.get('path'))
 
@@ -38,10 +38,10 @@ class DirectiveSerializer(serializers.ModelSerializer):
     class Meta:
         model = WebsiteDirective
         fields = ('name', 'value')
-    
+
     def to_representation(self, instance):
         return {prop.name: prop.value for prop in instance.all()}
-    
+
     def to_internal_value(self, data):
         return data
 
@@ -50,12 +50,12 @@ class WebsiteSerializer(AccountSerializerMixin, HyperlinkedModelSerializer):
     domains = RelatedDomainSerializer(many=True, required=False)
     contents = ContentSerializer(required=False, many=True, source='content_set')
     directives = DirectiveSerializer(required=False)
-    
+
     class Meta:
         model = Website
         fields = ('url', 'id', 'name', 'protocol', 'domains', 'is_active', 'contents', 'directives')
         postonly_fields = ('name',)
-    
+
     def validate(self, data):
         """ Prevent multiples domains on the same protocol """
         # Validate location and directive uniqueness
@@ -87,14 +87,14 @@ class WebsiteSerializer(AccountSerializerMixin, HyperlinkedModelSerializer):
         if errors:
             raise ValidationError(errors)
         return data
-    
+
     def create(self, validated_data):
         directives_data = validated_data.pop('directives')
         webapp = super(WebsiteSerializer, self).create(validated_data)
         for key, value in directives_data.items():
             WebsiteDirective.objects.create(webapp=webapp, name=key, value=value)
         return webap
-    
+
     def update_directives(self, instance, directives_data):
         existing = {}
         for obj in instance.directives.all():
@@ -112,13 +112,13 @@ class WebsiteSerializer(AccountSerializerMixin, HyperlinkedModelSerializer):
                     directive.save(update_fields=('value',))
         for to_delete in set(existing.keys())-posted:
             existing[to_delete].delete()
-    
+
     def update_contents(self, instance, contents_data):
         raise NotImplementedError
-    
+
     def update_domains(self, instance, domains_data):
         raise NotImplementedError
-    
+
     def update(self, instance, validated_data):
         directives_data = validated_data.pop('directives')
         domains_data = validated_data.pop('domains')
diff --git a/orchestra/permissions/options.py b/orchestra/permissions/options.py
index 74806885..b37d2363 100644
--- a/orchestra/permissions/options.py
+++ b/orchestra/permissions/options.py
@@ -7,24 +7,24 @@ import inspect
 
 
 class Permission(object):
-    """ 
+    """
     Base class used for defining class and instance permissions.
     Enabling an ''intuitive'' interface for checking permissions:
-        
+
         # Define permissions
         class NodePermission(Permission):
             def change(self, obj, cls, user):
                 return obj.user == user
-        
+
         # Provide permissions
         Node.has_permission = NodePermission()
-        
+
         # Check class permission by passing it as string
         Node.has_permission(user, 'change')
-        
+
         # Check class permission by calling it
         Node.has_permission.change(user)
-        
+
         # Check instance permissions
         node = Node()
         node.has_permission(user, 'change')
@@ -35,7 +35,7 @@ class Permission(object):
         # call interface: has_permission(user, 'perm')
         def call(user, perm):
             return getattr(self, perm)(obj, cls, user)
-        
+
         # has_permission.perm(user)
         for func in inspect.getmembers(type(self), predicate=inspect.ismethod):
             if not isinstance(self, func[1].__self__.__class__):
@@ -45,7 +45,7 @@ class Permission(object):
                 # self methods
                 setattr(call, func[0], functools.partial(func[1], self, obj, cls))
         return call
-    
+
     def _aggregate(self, obj, cls, perm):
         """ Aggregates cls methods to self class"""
         for method in inspect.getmembers(perm, predicate=inspect.ismethod):
@@ -68,7 +68,7 @@ class AllowAllPermission(object):
         """ Fake object that always returns True """
         def __call__(self, *args):
             return True
-        
+
         def __getattr__(self, name):
             return lambda n: True
 
@@ -76,13 +76,13 @@ class AllowAllPermission(object):
 class RelatedPermission(Permission):
     """
     Inherit permissions of a related object
-    
+
     The following example will inherit permissions from sliver_iface.sliver.slice
         SliverIfaces.has_permission = RelatedPermission('sliver.slices')
     """
     def __init__(self, relation):
         self.relation = relation
-    
+
     def __get__(self, obj, cls):
         """ Hacking object internals to provide means for the mentioned interface """
         # Walk through FK relations
@@ -90,17 +90,17 @@ class RelatedPermission(Permission):
         if obj is None:
             parent = cls
             for relation in relations:
-                parent = getattr(parent, relation).field.rel.to
+                parent = getattr(parent, relation).field.model
         else:
             parent = functools.reduce(getattr, relations, obj)
-        
+
         # call interface: has_permission(user, 'perm')
         def call(user, perm):
             return parent.has_permission(user, perm)
-        
+
         # method interface: has_permission.perm(user)
         for name, func in parent.has_permission.__dict__.items():
             if not name.startswith('_'):
                 setattr(call, name, func)
-        
+
         return call