diff --git a/taiga/auth/validators.py b/taiga/auth/validators.py
index 6c3661ed..a18dc4bc 100644
--- a/taiga/auth/validators.py
+++ b/taiga/auth/validators.py
@@ -17,11 +17,11 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 from django.core import validators as core_validators
-from django.core.exceptions import ValidationError
 from django.utils.translation import ugettext as _
 
 from taiga.base.api import serializers
 from taiga.base.api import validators
+from taiga.base.exceptions import ValidationError
 
 import re
 
@@ -39,8 +39,8 @@ class BaseRegisterValidator(validators.Validator):
         try:
             validator(value)
         except ValidationError:
-            raise serializers.ValidationError(_("Required. 255 characters or fewer. Letters, numbers "
-                                                "and /./-/_ characters'"))
+            raise ValidationError(_("Required. 255 characters or fewer. Letters, numbers "
+                                    "and /./-/_ characters'"))
         return attrs
 
 
diff --git a/taiga/base/api/fields.py b/taiga/base/api/fields.py
index 7dfa2c0a..fc4035c2 100644
--- a/taiga/base/api/fields.py
+++ b/taiga/base/api/fields.py
@@ -50,7 +50,6 @@ They are very similar to Django's form fields.
 from django import forms
 from django.conf import settings
 from django.core import validators
-from django.core.exceptions import ValidationError
 from django.db.models.fields import BLANK_CHOICE_DASH
 from django.forms import widgets
 from django.http import QueryDict
@@ -66,6 +65,8 @@ from django.utils.functional import Promise
 from django.utils.translation import ugettext
 from django.utils.translation import ugettext_lazy as _
 
+from taiga.base.exceptions import ValidationError
+
 from . import ISO_8601
 from .settings import api_settings
 
diff --git a/taiga/base/api/mixins.py b/taiga/base/api/mixins.py
index 861d77ec..c38b5cb7 100644
--- a/taiga/base/api/mixins.py
+++ b/taiga/base/api/mixins.py
@@ -44,12 +44,12 @@
 
 import warnings
 
-from django.core.exceptions import ValidationError
 from django.http import Http404
 from django.db import transaction as tx
 from django.utils.translation import ugettext as _
 
 from taiga.base import response
+from taiga.base.exceptions import ValidationError
 
 from .settings import api_settings
 from .utils import get_object_or_404
diff --git a/taiga/base/api/relations.py b/taiga/base/api/relations.py
index 60ba9a6e..6fbb98f5 100644
--- a/taiga/base/api/relations.py
+++ b/taiga/base/api/relations.py
@@ -48,7 +48,7 @@ Serializer fields that deal with relationships.
 These fields allow you to specify the style that should be used to represent
 model relationships, including hyperlinks, primary keys, or slugs.
 """
-from django.core.exceptions import ObjectDoesNotExist, ValidationError
+from django.core.exceptions import ObjectDoesNotExist
 from django.core.urlresolvers import resolve, get_script_prefix, NoReverseMatch
 from django import forms
 from django.db.models.fields import BLANK_CHOICE_DASH
@@ -59,6 +59,7 @@ from django.utils.translation import ugettext_lazy as _
 
 from .fields import Field, WritableField, get_component, is_simple_callable
 from .reverse import reverse
+from taiga.base.exceptions import ValidationError
 
 import warnings
 from urllib import parse as urlparse
diff --git a/taiga/base/api/serializers.py b/taiga/base/api/serializers.py
index 82565b26..f2dfd849 100644
--- a/taiga/base/api/serializers.py
+++ b/taiga/base/api/serializers.py
@@ -78,6 +78,8 @@ import serpy
 # This helps keep the separation between model fields, form fields, and
 # serializer fields more explicit.
 
+from taiga.base.exceptions import ValidationError
+
 from .relations import *
 from .fields import *
 
diff --git a/taiga/base/exceptions.py b/taiga/base/exceptions.py
index cc58ee6d..73d277ff 100644
--- a/taiga/base/exceptions.py
+++ b/taiga/base/exceptions.py
@@ -51,6 +51,7 @@ In addition Django's built in 403 and 404 exceptions are handled.
 """
 
 from django.core.exceptions import PermissionDenied as DjangoPermissionDenied
+from django.core.exceptions import ValidationError as DjangoValidationError
 from django.utils.encoding import force_text
 from django.utils.translation import ugettext_lazy as _
 from django.http import Http404
@@ -224,6 +225,7 @@ class NotEnoughSlotsForProject(BaseException):
             "total_memberships": total_memberships
         }
 
+
 def format_exception(exc):
     if isinstance(exc.detail, (dict, list, tuple,)):
         detail = exc.detail
@@ -270,3 +272,6 @@ def exception_handler(exc):
 
     # Note: Unhandled exceptions will raise a 500 error.
     return None
+
+
+ValidationError = DjangoValidationError
diff --git a/taiga/export_import/serializers/fields.py b/taiga/export_import/serializers/fields.py
index 64c01436..9ed21a19 100644
--- a/taiga/export_import/serializers/fields.py
+++ b/taiga/export_import/serializers/fields.py
@@ -23,11 +23,11 @@ from collections import OrderedDict
 
 from django.core.files.base import ContentFile
 from django.core.exceptions import ObjectDoesNotExist
-from django.core.exceptions import ValidationError
 from django.utils.translation import ugettext as _
 from django.contrib.contenttypes.models import ContentType
 
 from taiga.base.api import serializers
+from taiga.base.exceptions import ValidationError
 from taiga.base.fields import JsonField
 from taiga.mdrender.service import render as mdrender
 from taiga.users import models as users_models
diff --git a/taiga/export_import/serializers/serializers.py b/taiga/export_import/serializers/serializers.py
index 7cf46cba..6a316b68 100644
--- a/taiga/export_import/serializers/serializers.py
+++ b/taiga/export_import/serializers/serializers.py
@@ -16,13 +16,11 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-import copy
-
-from django.core.exceptions import ValidationError
 from django.utils.translation import ugettext as _
 
 from taiga.base.api import serializers
 from taiga.base.fields import JsonField, PgArrayField
+from taiga.base.exceptions import ValidationError
 
 from taiga.projects import models as projects_models
 from taiga.projects.custom_attributes import models as custom_attributes_models
@@ -31,15 +29,12 @@ from taiga.projects.tasks import models as tasks_models
 from taiga.projects.issues import models as issues_models
 from taiga.projects.milestones import models as milestones_models
 from taiga.projects.wiki import models as wiki_models
-from taiga.projects.history import models as history_models
-from taiga.projects.attachments import models as attachments_models
 from taiga.timeline import models as timeline_models
 from taiga.users import models as users_models
 from taiga.projects.votes import services as votes_service
 
-from .fields import (FileField, RelatedNoneSafeField, UserRelatedField,
-                     UserPkField, CommentField, ProjectRelatedField,
-                     HistoryUserField, HistoryValuesField, HistoryDiffField,
+from .fields import (FileField, UserRelatedField,
+                     ProjectRelatedField,
                      TimelineDataField, ContentTypeField)
 from .mixins import (HistoryExportSerializerMixin,
                      AttachmentExportSerializerMixin,
@@ -125,7 +120,7 @@ class IssueCustomAttributeExportSerializer(serializers.ModelSerializer):
 
 
 class BaseCustomAttributesValuesExportSerializer(serializers.ModelSerializer):
-    attributes_values = JsonField(source="attributes_values",required=True)
+    attributes_values = JsonField(source="attributes_values", required=True)
     _custom_attribute_model = None
     _container_field = None
 
@@ -158,6 +153,7 @@ class BaseCustomAttributesValuesExportSerializer(serializers.ModelSerializer):
 
         return attrs
 
+
 class UserStoryCustomAttributesValuesExportSerializer(BaseCustomAttributesValuesExportSerializer):
     _custom_attribute_model = custom_attributes_models.UserStoryCustomAttribute
     _container_model = "userstories.UserStory"
@@ -224,7 +220,7 @@ class MilestoneExportSerializer(WatcheableObjectModelSerializerMixin):
         name = attrs[source]
         qs = self.project.milestones.filter(name=name)
         if qs.exists():
-            raise serializers.ValidationError(_("Name duplicated for the project"))
+            raise ValidationError(_("Name duplicated for the project"))
 
         return attrs
 
@@ -268,7 +264,9 @@ class UserStoryExportSerializer(CustomAttributesValuesExportSerializerMixin, His
 
     def custom_attributes_queryset(self, project):
         if project.id not in _custom_userstories_attributes_cache:
-            _custom_userstories_attributes_cache[project.id] = list(project.userstorycustomattributes.all().values('id', 'name'))
+            _custom_userstories_attributes_cache[project.id] = list(
+                project.userstorycustomattributes.all().values('id', 'name')
+            )
         return _custom_userstories_attributes_cache[project.id]
 
 
@@ -314,10 +312,10 @@ class WikiLinkExportSerializer(serializers.ModelSerializer):
         exclude = ('id', 'project')
 
 
-
 class TimelineExportSerializer(serializers.ModelSerializer):
     data = TimelineDataField()
     data_content_type = ContentTypeField()
+
     class Meta:
         model = timeline_models.Timeline
         exclude = ('id', 'project', 'namespace', 'object_id', 'content_type')
diff --git a/taiga/projects/api.py b/taiga/projects/api.py
index c441e419..6445c17f 100644
--- a/taiga/projects/api.py
+++ b/taiga/projects/api.py
@@ -22,7 +22,6 @@ from dateutil.relativedelta import relativedelta
 
 from django.apps import apps
 from django.conf import settings
-from django.core.exceptions import ValidationError
 from django.http import Http404
 from django.utils.translation import ugettext as _
 from django.utils import timezone
@@ -651,7 +650,7 @@ class MembershipViewSet(BlockedByProjectMixin, ModelCrudViewSet):
                                                       invitation_extra_text=invitation_extra_text,
                                                       callback=self.post_save,
                                                       precall=self.pre_save)
-        except ValidationError as err:
+        except exc.ValidationError as err:
             return response.BadRequest(err.message_dict)
 
         members_serialized = self.admin_serializer_class(members, many=True)
diff --git a/taiga/projects/custom_attributes/validators.py b/taiga/projects/custom_attributes/validators.py
index 506c040c..6663de5d 100644
--- a/taiga/projects/custom_attributes/validators.py
+++ b/taiga/projects/custom_attributes/validators.py
@@ -20,7 +20,7 @@
 from django.utils.translation import ugettext_lazy as _
 
 from taiga.base.fields import JsonField
-from taiga.base.api.serializers import ValidationError
+from taiga.base.exceptions import ValidationError
 from taiga.base.api.validators import ModelValidator
 
 from . import models
diff --git a/taiga/projects/milestones/validators.py b/taiga/projects/milestones/validators.py
index 8de3174c..b7d4d484 100644
--- a/taiga/projects/milestones/validators.py
+++ b/taiga/projects/milestones/validators.py
@@ -18,7 +18,7 @@
 
 from django.utils.translation import ugettext as _
 
-from taiga.base.api import serializers
+from taiga.base.exceptions import ValidationError
 from taiga.base.api import validators
 from taiga.projects.validators import DuplicatedNameInProjectValidator
 from taiga.projects.notifications.validators import WatchersValidator
@@ -31,7 +31,7 @@ class MilestoneExistsValidator:
         value = attrs[source]
         if not models.Milestone.objects.filter(pk=value).exists():
             msg = _("There's no milestone with that id")
-            raise serializers.ValidationError(msg)
+            raise ValidationError(msg)
         return attrs
 
 
diff --git a/taiga/projects/notifications/validators.py b/taiga/projects/notifications/validators.py
index 851cc309..40e02083 100644
--- a/taiga/projects/notifications/validators.py
+++ b/taiga/projects/notifications/validators.py
@@ -18,7 +18,7 @@
 
 from django.utils.translation import ugettext as _
 
-from taiga.base.api import serializers
+from taiga.base.exceptions import ValidationError
 
 
 class WatchersValidator:
@@ -45,6 +45,6 @@ class WatchersValidator:
         existing_watcher_ids = project.get_watchers().values_list("id", flat=True)
         result = set(users).difference(member_ids).difference(existing_watcher_ids)
         if result:
-            raise serializers.ValidationError(_("Watchers contains invalid users"))
+            raise ValidationError(_("Watchers contains invalid users"))
 
         return attrs
diff --git a/taiga/projects/references/validators.py b/taiga/projects/references/validators.py
index 5fcefee8..85456c4c 100644
--- a/taiga/projects/references/validators.py
+++ b/taiga/projects/references/validators.py
@@ -18,6 +18,7 @@
 
 from taiga.base.api import serializers
 from taiga.base.api import validators
+from taiga.base.exceptions import ValidationError
 
 
 class ResolverValidator(validators.Validator):
@@ -32,10 +33,10 @@ class ResolverValidator(validators.Validator):
     def validate(self, attrs):
         if "ref" in attrs:
             if "us" in attrs:
-                raise serializers.ValidationError("'us' param is incompatible with 'ref' in the same request")
+                raise ValidationError("'us' param is incompatible with 'ref' in the same request")
             if "task" in attrs:
-                raise serializers.ValidationError("'task' param is incompatible with 'ref' in the same request")
+                raise ValidationError("'task' param is incompatible with 'ref' in the same request")
             if "issue" in attrs:
-                raise serializers.ValidationError("'issue' param is incompatible with 'ref' in the same request")
+                raise ValidationError("'issue' param is incompatible with 'ref' in the same request")
 
         return attrs
diff --git a/taiga/projects/tagging/fields.py b/taiga/projects/tagging/fields.py
index 24f92f23..47553d8c 100644
--- a/taiga/projects/tagging/fields.py
+++ b/taiga/projects/tagging/fields.py
@@ -16,11 +16,11 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-from django.core.exceptions import ValidationError
 from django.forms import widgets
 from django.utils.translation import ugettext_lazy as _
 
 from taiga.base.api import serializers
+from taiga.base.exceptions import ValidationError
 
 import re
 
diff --git a/taiga/projects/tasks/validators.py b/taiga/projects/tasks/validators.py
index 7f71636c..ddb3f33b 100644
--- a/taiga/projects/tasks/validators.py
+++ b/taiga/projects/tasks/validators.py
@@ -20,6 +20,7 @@ from django.utils.translation import ugettext as _
 
 from taiga.base.api import serializers
 from taiga.base.api import validators
+from taiga.base.exceptions import ValidationError
 from taiga.base.fields import PgArrayField
 from taiga.projects.milestones.validators import MilestoneExistsValidator
 from taiga.projects.notifications.mixins import EditableWatchedResourceSerializer
@@ -34,7 +35,7 @@ class TaskExistsValidator:
         value = attrs[source]
         if not models.Task.objects.filter(pk=value).exists():
             msg = _("There's no task with that id")
-            raise serializers.ValidationError(msg)
+            raise ValidationError(msg)
         return attrs
 
 
diff --git a/taiga/projects/userstories/validators.py b/taiga/projects/userstories/validators.py
index 4ea0b24a..2d61934f 100644
--- a/taiga/projects/userstories/validators.py
+++ b/taiga/projects/userstories/validators.py
@@ -21,6 +21,7 @@ from django.utils.translation import ugettext as _
 from taiga.base.api import serializers
 from taiga.base.api import validators
 from taiga.base.api.utils import get_object_or_404
+from taiga.base.exceptions import ValidationError
 from taiga.base.fields import PgArrayField
 from taiga.base.fields import PickledObjectField
 from taiga.projects.milestones.validators import MilestoneExistsValidator
@@ -40,7 +41,7 @@ class UserStoryExistsValidator:
         value = attrs[source]
         if not models.UserStory.objects.filter(pk=value).exists():
             msg = _("There's no user story with that id")
-            raise serializers.ValidationError(msg)
+            raise ValidationError(msg)
         return attrs
 
 
@@ -105,9 +106,9 @@ class UpdateMilestoneBulkValidator(ProjectExistsValidator, MilestoneExistsValida
         project = get_object_or_404(Project, pk=data["project_id"])
 
         if project.user_stories.filter(id__in=user_story_ids).count() != len(user_story_ids):
-            raise serializers.ValidationError("all the user stories must be from the same project")
+            raise ValidationError("all the user stories must be from the same project")
 
         if project.milestones.filter(id=data["milestone_id"]).count() != 1:
-            raise serializers.ValidationError("the milestone isn't valid for the project")
+            raise ValidationError("the milestone isn't valid for the project")
 
         return data
diff --git a/taiga/projects/validators.py b/taiga/projects/validators.py
index c8ab21bb..de06c05c 100644
--- a/taiga/projects/validators.py
+++ b/taiga/projects/validators.py
@@ -21,6 +21,7 @@ from django.utils.translation import ugettext as _
 
 from taiga.base.api import serializers
 from taiga.base.api import validators
+from taiga.base.exceptions import ValidationError
 from taiga.base.fields import JsonField
 from taiga.base.fields import PgArrayField
 from taiga.users.validators import RoleExistsValidator
@@ -49,7 +50,7 @@ class DuplicatedNameInProjectValidator:
             qs = model.objects.filter(project=attrs["project"], name=attrs[source])
 
         if qs and qs.exists():
-            raise serializers.ValidationError(_("Name duplicated for the project"))
+            raise ValidationError(_("Name duplicated for the project"))
 
         return attrs
 
@@ -59,7 +60,7 @@ class ProjectExistsValidator:
         value = attrs[source]
         if not models.Project.objects.filter(pk=value).exists():
             msg = _("There's no project with that id")
-            raise serializers.ValidationError(msg)
+            raise ValidationError(msg)
         return attrs
 
 
@@ -68,7 +69,7 @@ class UserStoryStatusExistsValidator:
         value = attrs[source]
         if not models.UserStoryStatus.objects.filter(pk=value).exists():
             msg = _("There's no user story status with that id")
-            raise serializers.ValidationError(msg)
+            raise ValidationError(msg)
         return attrs
 
 
@@ -77,7 +78,7 @@ class TaskStatusExistsValidator:
         value = attrs[source]
         if not models.TaskStatus.objects.filter(pk=value).exists():
             msg = _("There's no task status with that id")
-            raise serializers.ValidationError(msg)
+            raise ValidationError(msg)
         return attrs
 
 
@@ -152,7 +153,7 @@ class MembershipValidator(validators.ModelValidator):
                        Q(project_id=project.id, email=email))
 
         if qs.count() > 0:
-            raise serializers.ValidationError(_("Email address is already taken"))
+            raise ValidationError(_("Email address is already taken"))
 
         return attrs
 
@@ -164,7 +165,7 @@ class MembershipValidator(validators.ModelValidator):
         role = attrs[source]
 
         if project.roles.filter(id=role.id).count() == 0:
-            raise serializers.ValidationError(_("Invalid role for the project"))
+            raise ValidationError(_("Invalid role for the project"))
 
         return attrs
 
@@ -175,10 +176,10 @@ class MembershipValidator(validators.ModelValidator):
 
         if (self.object and self.object.user):
             if self.object.user.id == project.owner_id and not attrs[source]:
-                raise serializers.ValidationError(_("The project owner must be admin."))
+                raise ValidationError(_("The project owner must be admin."))
 
             if not services.project_has_valid_admins(project, exclude_user=self.object.user):
-                raise serializers.ValidationError(
+                raise ValidationError(
                     _("At least one user must be an active admin for this project.")
                 )
 
diff --git a/taiga/users/serializers.py b/taiga/users/serializers.py
index 75daa74e..a28f5ce3 100644
--- a/taiga/users/serializers.py
+++ b/taiga/users/serializers.py
@@ -17,9 +17,6 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 from django.conf import settings
-from django.core import validators
-from django.core.exceptions import ValidationError
-from django.utils.translation import ugettext_lazy as _
 
 from taiga.base.api import serializers
 from taiga.base.fields import PgArrayField, Field, MethodField, I18NField
@@ -27,14 +24,11 @@ from taiga.base.fields import PgArrayField, Field, MethodField, I18NField
 from taiga.base.utils.thumbnails import get_thumbnail_url
 
 from taiga.projects.models import Project
-from .models import User, Role
 from .services import get_photo_or_gravatar_url, get_big_photo_or_gravatar_url
 from .gravatar import get_gravatar_url
 
 from collections import namedtuple
 
-import re
-
 
 ######################################################
 # User
diff --git a/taiga/users/validators.py b/taiga/users/validators.py
index 11e78efb..f23da47a 100644
--- a/taiga/users/validators.py
+++ b/taiga/users/validators.py
@@ -17,12 +17,12 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 from django.core import validators as core_validators
-from django.core.exceptions import ValidationError
 from django.utils.translation import ugettext_lazy as _
 
 from taiga.base.api import serializers
 from taiga.base.api import validators
-from taiga.base.fields import PgArrayField, Field
+from taiga.base.exceptions import ValidationError
+from taiga.base.fields import PgArrayField
 
 from .models import User, Role
 
@@ -34,7 +34,7 @@ class RoleExistsValidator:
         value = attrs[source]
         if not Role.objects.filter(pk=value).exists():
             msg = _("There's no role with that id")
-            raise serializers.ValidationError(msg)
+            raise ValidationError(msg)
         return attrs
 
 
@@ -55,13 +55,13 @@ class UserValidator(validators.ModelValidator):
         try:
             validator(value)
         except ValidationError:
-            raise validators.ValidationError(_("Required. 255 characters or fewer. Letters, "
-                                                "numbers and /./-/_ characters'"))
+            raise ValidationError(_("Required. 255 characters or fewer. Letters, "
+                                    "numbers and /./-/_ characters'"))
 
         if (self.object and
                 self.object.username != value and
                 User.objects.filter(username=value).exists()):
-            raise validators.ValidationError(_("Invalid username. Try with a different one."))
+            raise ValidationError(_("Invalid username. Try with a different one."))
 
         return attrs
 
diff --git a/taiga/userstorage/api.py b/taiga/userstorage/api.py
index 5b097e71..94c5ea00 100644
--- a/taiga/userstorage/api.py
+++ b/taiga/userstorage/api.py
@@ -19,7 +19,6 @@
 from django.utils.translation import ugettext as _
 
 from taiga.base.api import ModelCrudViewSet
-from taiga.base.api.serializers import ValidationError
 from taiga.base import exceptions as exc
 
 from . import models