diff --git a/django/db/migrations/writer.py b/django/db/migrations/writer.py
index b1650b27be..a0ff149372 100644
--- a/django/db/migrations/writer.py
+++ b/django/db/migrations/writer.py
@@ -194,7 +194,7 @@ class MigrationWriter(object):
             if isinstance(value, set):
                 format = "set([%s])"
             elif isinstance(value, tuple):
-                format = "(%s)" if len(value) else "(%s,)"
+                format = "(%s)" if len(value) > 1 else "(%s,)"
             else:
                 format = "[%s]"
             return format % (", ".join(strings)), imports
diff --git a/django/db/models/base.py b/django/db/models/base.py
index 141d28eb7f..c9187c10dc 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -251,7 +251,10 @@ class ModelBase(type):
                     attr_name = '%s_ptr' % base._meta.model_name
                     field = OneToOneField(base, name=attr_name,
                             auto_created=True, parent_link=True)
-                    new_class.add_to_class(attr_name, field)
+                    # Only add the ptr field if it's not already present;
+                    # e.g. migrations will already have it specified
+                    if not hasattr(new_class, attr_name):
+                        new_class.add_to_class(attr_name, field)
                 else:
                     field = None
                 new_class._meta.parents[base] = field
diff --git a/tests/migrations/test_operations.py b/tests/migrations/test_operations.py
index f60c1a27e7..96dc7d0610 100644
--- a/tests/migrations/test_operations.py
+++ b/tests/migrations/test_operations.py
@@ -90,6 +90,38 @@ class OperationTests(MigrationTestBase):
         self.assertEqual(len(definition[2]), 0)
         self.assertEqual(definition[1][0], "Pony")
 
+    def test_create_model_inheritance(self):
+        """
+        Tests the CreateModel operation on a multi-table inheritance setup.
+        """
+        project_state = self.set_up_test_model("test_crmoih")
+        # Test the state alteration
+        operation = migrations.CreateModel(
+            "ShetlandPony",
+            [
+                ('pony_ptr', models.OneToOneField(
+                    auto_created=True,
+                    primary_key=True,
+                    to_field=u'id',
+                    serialize=False,
+                    to='test_crmoih.Pony',
+                )),
+                ("cuteness", models.IntegerField(default=1)),
+            ],
+        )
+        new_state = project_state.clone()
+        operation.state_forwards("test_crmoih", new_state)
+        self.assertIn(("test_crmoih", "shetlandpony"), new_state.models)
+        # Test the database alteration
+        self.assertTableNotExists("test_crmoih_shetlandpony")
+        with connection.schema_editor() as editor:
+            operation.database_forwards("test_crmoih", editor, project_state, new_state)
+        self.assertTableExists("test_crmoih_shetlandpony")
+        # And test reversal
+        with connection.schema_editor() as editor:
+            operation.database_backwards("test_crmoih", editor, new_state, project_state)
+        self.assertTableNotExists("test_crmoih_shetlandpony")
+
     def test_delete_model(self):
         """
         Tests the DeleteModel operation.
diff --git a/tests/migrations/test_state.py b/tests/migrations/test_state.py
index e2d970e0f5..4e01613278 100644
--- a/tests/migrations/test_state.py
+++ b/tests/migrations/test_state.py
@@ -33,6 +33,12 @@ class StateTests(TestCase):
                 proxy = True
                 ordering = ["name"]
 
+        class SubAuthor(Author):
+            width = models.FloatField(null=True)
+            class Meta:
+                app_label = "migrations"
+                apps = new_apps
+
         class Book(models.Model):
             title = models.CharField(max_length=1000)
             author = models.ForeignKey(Author)
@@ -47,6 +53,7 @@ class StateTests(TestCase):
         project_state = ProjectState.from_apps(new_apps)
         author_state = project_state.models['migrations', 'author']
         author_proxy_state = project_state.models['migrations', 'authorproxy']
+        sub_author_state = project_state.models['migrations', 'subauthor']
         book_state = project_state.models['migrations', 'book']
 
         self.assertEqual(author_state.app_label, "migrations")
@@ -55,7 +62,7 @@ class StateTests(TestCase):
         self.assertEqual(author_state.fields[1][1].max_length, 255)
         self.assertEqual(author_state.fields[2][1].null, False)
         self.assertEqual(author_state.fields[3][1].null, True)
-        self.assertEqual(author_state.options, {"unique_together": {("name", "bio")}})
+        self.assertEqual(author_state.options, {"unique_together": set([("name", "bio")])})
         self.assertEqual(author_state.bases, (models.Model, ))
 
         self.assertEqual(book_state.app_label, "migrations")
@@ -73,6 +80,11 @@ class StateTests(TestCase):
         self.assertEqual(author_proxy_state.options, {"proxy": True, "ordering": ["name"]})
         self.assertEqual(author_proxy_state.bases, ("migrations.author", ))
 
+        self.assertEqual(sub_author_state.app_label, "migrations")
+        self.assertEqual(sub_author_state.name, "SubAuthor")
+        self.assertEqual(len(sub_author_state.fields), 2)
+        self.assertEqual(sub_author_state.bases, ("migrations.author", ))
+
     def test_render(self):
         """
         Tests rendering a ProjectState into an Apps.
@@ -89,10 +101,27 @@ class StateTests(TestCase):
             {},
             None,
         ))
+        project_state.add_model_state(ModelState(
+            "migrations",
+            "SubTag",
+            [
+                ('tag_ptr', models.OneToOneField(
+                    auto_created=True,
+                    primary_key=True,
+                    to_field=u'id',
+                    serialize=False,
+                    to='migrations.Tag',
+                )),
+                ("awesome", models.BooleanField()),
+            ],
+            options={},
+            bases=("migrations.Tag",),
+        ))
 
         new_apps = project_state.render()
         self.assertEqual(new_apps.get_model("migrations", "Tag")._meta.get_field_by_name("name")[0].max_length, 100)
         self.assertEqual(new_apps.get_model("migrations", "Tag")._meta.get_field_by_name("hidden")[0].null, False)
+        self.assertEqual(len(new_apps.get_model("migrations", "SubTag")._meta.local_fields), 2)
 
     def test_render_model_inheritance(self):
         class Book(models.Model):