diff --git a/taiga/projects/issues/models.py b/taiga/projects/issues/models.py
index c289581b..dd92a771 100644
--- a/taiga/projects/issues/models.py
+++ b/taiga/projects/issues/models.py
@@ -28,7 +28,7 @@ from taiga.projects.occ import OCCModelMixin
 from taiga.projects.mixins.blocked import BlockedMixin
 
 
-class Issue(OCCModelMixin, WatchedModelMixin, BlockedMixin, TaggedMixin):
+class Issue(OCCModelMixin, WatchedModelMixin, BlockedMixin, TaggedMixin, models.Model):
     ref = models.BigIntegerField(db_index=True, null=True, blank=True, default=None,
                                  verbose_name=_("ref"))
     owner = models.ForeignKey(settings.AUTH_USER_MODEL, null=True, blank=True, default=None,
diff --git a/taiga/projects/models.py b/taiga/projects/models.py
index ff1d3a10..613e1b0c 100644
--- a/taiga/projects/models.py
+++ b/taiga/projects/models.py
@@ -110,7 +110,7 @@ class ProjectDefaults(models.Model):
         abstract = True
 
 
-class Project(ProjectDefaults, TaggedMixin):
+class Project(ProjectDefaults, TaggedMixin, models.Model):
     name = models.CharField(max_length=250, unique=True, null=False, blank=False,
                             verbose_name=_("name"))
     slug = models.SlugField(max_length=250, unique=True, null=False, blank=True,
diff --git a/taiga/projects/tasks/models.py b/taiga/projects/tasks/models.py
index f27a0f86..f4b0d12f 100644
--- a/taiga/projects/tasks/models.py
+++ b/taiga/projects/tasks/models.py
@@ -30,7 +30,7 @@ from taiga.projects.milestones.models import Milestone
 from taiga.projects.mixins.blocked import BlockedMixin
 
 
-class Task(OCCModelMixin, WatchedModelMixin, BlockedMixin, TaggedMixin):
+class Task(OCCModelMixin, WatchedModelMixin, BlockedMixin, TaggedMixin, models.Model):
     user_story = models.ForeignKey("userstories.UserStory", null=True, blank=True,
                                    related_name="tasks", verbose_name=_("user story"))
     ref = models.BigIntegerField(db_index=True, null=True, blank=True, default=None,
diff --git a/taiga/projects/userstories/models.py b/taiga/projects/userstories/models.py
index aa0212d2..3d9a2cf5 100644
--- a/taiga/projects/userstories/models.py
+++ b/taiga/projects/userstories/models.py
@@ -51,7 +51,7 @@ class RolePoints(models.Model):
         return "{}: {}".format(self.role.name, self.points.name)
 
 
-class UserStory(OCCModelMixin, WatchedModelMixin, BlockedMixin, TaggedMixin):
+class UserStory(OCCModelMixin, WatchedModelMixin, BlockedMixin, TaggedMixin, models.Model):
 
     ref = models.BigIntegerField(db_index=True, null=True, blank=True, default=None,
                                  verbose_name=_("ref"))
diff --git a/tests/integration/test_tags.py b/tests/integration/test_tags.py
index 987d26d8..56eb76c4 100644
--- a/tests/integration/test_tags.py
+++ b/tests/integration/test_tags.py
@@ -1,11 +1,13 @@
 import pytest
 
+from django.db import models
+
 from taiga.base import tags
 
 pytestmark = pytest.mark.django_db
 
 
-class TaggedModel(tags.TaggedMixin):
+class TaggedModel(tags.TaggedMixin, models.Model):
     class Meta:
         app_label = "base"