diff --git a/.gitignore b/.gitignore
index bab3b71..c18fed3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -17,3 +17,4 @@ dist/
 docs/_build/
 htmlcov/
 venv/
+.venv/
diff --git a/polymorphic/tests/migrations/0001_initial.py b/polymorphic/tests/migrations/0001_initial.py
index 4707a36..38106a3 100644
--- a/polymorphic/tests/migrations/0001_initial.py
+++ b/polymorphic/tests/migrations/0001_initial.py
@@ -1450,6 +1450,13 @@ class Migration(migrations.Migration):
                 to="tests.ParentModelWithManager",
             ),
         ),
+        migrations.AddField(
+            model_name="childmodelwithmanager",
+            name="field1",
+            field=models.CharField(
+                max_length=10,
+            ),
+        ),
         migrations.AddField(
             model_name="childmodelwithmanager",
             name="polymorphic_ctype",
diff --git a/polymorphic/tests/models.py b/polymorphic/tests/models.py
index 96e361f..494b98f 100644
--- a/polymorphic/tests/models.py
+++ b/polymorphic/tests/models.py
@@ -222,6 +222,7 @@ class ParentModelWithManager(PolymorphicModel):
 
 class ChildModelWithManager(PolymorphicModel):
     # Also test whether foreign keys receive the manager:
+    field1 = models.CharField(max_length=10)  # needed as MyManager uses it
     fk = models.ForeignKey(
         ParentModelWithManager, on_delete=models.CASCADE, related_name="childmodel_set"
     )
diff --git a/polymorphic/tests/test_multidb.py b/polymorphic/tests/test_multidb.py
index b70a8d5..dee08d4 100644
--- a/polymorphic/tests/test_multidb.py
+++ b/polymorphic/tests/test_multidb.py
@@ -18,7 +18,7 @@ from polymorphic.tests.models import (
 
 
 class MultipleDatabasesTests(TestCase):
-    multi_db = True
+    databases = ["default", "secondary"]
 
     def test_save_to_non_default_database(self):
         Model2A.objects.db_manager("secondary").create(field1="A1")
diff --git a/polymorphic/tests/test_orm.py b/polymorphic/tests/test_orm.py
index a0fd1e8..84da2a5 100644
--- a/polymorphic/tests/test_orm.py
+++ b/polymorphic/tests/test_orm.py
@@ -481,21 +481,22 @@ class PolymorphicTests(TransactionTestCase):
     def test_foreignkey_field(self):
         self.create_model2abcd()
 
-        object2a = Model2A.base_objects.get(field1="C1")
+        object2a = Model2A.objects.get(field1="C1")
         self.assertEqual(object2a.model2b.__class__, Model2B)
 
-        object2b = Model2B.base_objects.get(field1="C1")
+        object2b = Model2B.objects.get(field1="C1")
         self.assertEqual(object2b.model2c.__class__, Model2C)
 
     def test_onetoone_field(self):
         self.create_model2abcd()
 
+        # FIXME: We should not use base_objects here.
         a = Model2A.base_objects.get(field1="C1")
         b = One2OneRelatingModelDerived.objects.create(
             one2one=a, field1="f1", field2="f2"
         )
 
-        # this result is basically wrong, probably due to Django cacheing (we used base_objects), but should not be a problem
+        # FIXME: this result is basically wrong, probably due to Django cacheing (we used base_objects), but should not be a problem
         self.assertEqual(b.one2one.__class__, Model2A)
         self.assertEqual(b.one2one_id, b.one2one.id)
 
@@ -808,7 +809,6 @@ class PolymorphicTests(TransactionTestCase):
 
         self.assertIs(type(ModelWithMyManager.objects), MyManager)
         self.assertIs(type(ModelWithMyManager._default_manager), MyManager)
-        self.assertIs(type(ModelWithMyManager.base_objects), models.Manager)
 
     def test_user_defined_manager_as_secondary(self):
         self.create_model2abcd()
@@ -831,7 +831,6 @@ class PolymorphicTests(TransactionTestCase):
         self.assertIs(
             type(ModelWithMyManagerNoDefault._default_manager), PolymorphicManager
         )
-        self.assertIs(type(ModelWithMyManagerNoDefault.base_objects), models.Manager)
 
     def test_user_objects_manager_as_secondary(self):
         self.create_model2abcd()
@@ -841,7 +840,6 @@ class PolymorphicTests(TransactionTestCase):
         self.assertIs(type(ModelWithMyManagerDefault.my_objects), MyManager)
         self.assertIs(type(ModelWithMyManagerDefault.objects), PolymorphicManager)
         self.assertIs(type(ModelWithMyManagerDefault._default_manager), MyManager)
-        self.assertIs(type(ModelWithMyManagerDefault.base_objects), models.Manager)
 
     def test_user_defined_queryset_as_manager(self):
         self.create_model2abcd()
@@ -864,7 +862,6 @@ class PolymorphicTests(TransactionTestCase):
             type(ModelWithMyManager2._default_manager).__name__,
             "PolymorphicManagerFromMyManagerQuerySet",
         )
-        self.assertIs(type(ModelWithMyManager2.base_objects), models.Manager)
 
     def test_manager_inheritance(self):
         # by choice of MRO, should be MyManager from MROBase1.
diff --git a/tox.ini b/tox.ini
index e507416..2e4d2c3 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,9 +1,9 @@
 [tox]
 envlist =
-	py35-django{21,22,master}
-	py36-django{21,22,30,31,master}
-	py37-django{21,22,30,31,master}
-	py38-django{21,22,30,31,master}
+	py35-django{21,22}
+	py36-django{21,22,30,31}
+	py37-django{21,22,30,31}
+	py38-django{21,22,30,31}
 	docs
 
 [testenv]
@@ -12,6 +12,7 @@ setenv =
 	postgres: DEFAULT_DATABASE = postgres:///default
 	postgres: SECONDARY_DATABASE = postgres:///secondary
 deps =
+	ipdb
 	coverage
 	dj-database-url
 	django21: Django ~= 2.1