diff --git a/polymorphic/models.py b/polymorphic/models.py
index 0b2cb92..e2bb0a2 100644
--- a/polymorphic/models.py
+++ b/polymorphic/models.py
@@ -107,12 +107,14 @@ class PolymorphicModel(six.with_metaclass(PolymorphicModelBase, models.Model)):
 
         # Protect against bad imports (dumpdata without --natural) or other
         # issues missing with the ContentType models.
-        if model is not None \
-                and not issubclass(model, self.__class__) \
-                and not issubclass(model, self.__class__._meta.proxy_for_model):
-            raise PolymorphicTypeInvalid("ContentType {0} for {1} #{2} does not point to a subclass!".format(
-                self.polymorphic_ctype_id, model, self.pk,
-            ))
+        if model is not None and not issubclass(model, self.__class__):
+            if self.__class__._meta.proxy_for_model is None or \
+                    not issubclass(model, self.__class__._meta.proxy_for_model):
+
+                raise PolymorphicTypeInvalid("ContentType {0} for {1} #{2} does not point to a subclass!".format(
+                    self.polymorphic_ctype_id, model, self.pk,
+                ))
+
         return model
 
     def get_real_concrete_instance_class_id(self):
diff --git a/polymorphic/tests/models.py b/polymorphic/tests/models.py
index 2ea89d5..c74ae1e 100644
--- a/polymorphic/tests/models.py
+++ b/polymorphic/tests/models.py
@@ -218,7 +218,7 @@ class ChildModelWithManager(PolymorphicModel):
 class PlainMyManagerQuerySet(QuerySet):
 
     def my_queryset_foo(self):
-        return self.all()  # Just a method to prove the existance of the custom queryset.
+        return self.all()  # Just a method to prove the existence of the custom queryset.
 
 
 class PlainMyManager(models.Manager):
diff --git a/polymorphic/tests/test_orm.py b/polymorphic/tests/test_orm.py
index 557e370..3c70e28 100644
--- a/polymorphic/tests/test_orm.py
+++ b/polymorphic/tests/test_orm.py
@@ -4,12 +4,12 @@ import uuid
 from django.contrib.contenttypes.models import ContentType
 from django.db import models
 from django.db.models import Case, Count, Q, When
-from django.test import TestCase, TransactionTestCase
+from django.test import TransactionTestCase
 from django.utils import six
 
 from polymorphic import query_translate
 from polymorphic.managers import PolymorphicManager
-from polymorphic.models import PolymorphicTypeUndefined
+from polymorphic.models import PolymorphicTypeInvalid, PolymorphicTypeUndefined
 from polymorphic.tests.models import (
     ArtProject,
     Base,
@@ -68,7 +68,6 @@ from polymorphic.tests.models import (
     ProxyModelA,
     ProxyModelB,
     ProxyModelBase,
-    QuerySet,
     RedheadDuck,
     RelationA,
     RelationB,
@@ -975,6 +974,17 @@ class PolymorphicTests(TransactionTestCase):
         with self.assertRaises(PolymorphicTypeUndefined):
             list(Model2A.objects.all())
 
+    def test_invalid_polymorphic_id(self):
+        """Test that a proper error message is displayed when the database ``polymorphic_ctype_id`` is invalid"""
+        Model2A.objects.create(field1='A1')
+        Model2B.objects.create(field1='A1', field2='B2')
+        Model2B.objects.create(field1='A1', field2='B2')
+        invalid = ContentType.objects.get_for_model(PlainA).pk
+        Model2A.objects.all().update(polymorphic_ctype_id=invalid)
+
+        with self.assertRaises(PolymorphicTypeInvalid):
+            list(Model2A.objects.all())
+
     def test_bulk_create_abstract_inheritance(self):
         ArtProject.objects.bulk_create([
             ArtProject(topic='Painting with Tim', artist='T. Turner'),