diff --git a/django/db/models/base.py b/django/db/models/base.py
index 60b98ec739..462483d058 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -612,7 +612,7 @@ class Model(object):
 
         for related in self._meta.get_all_related_many_to_many_objects():
             if related.field.rel.through:
-                db = router.db_for_write(related.field.rel.through.__class__, instance=self)
+                db = router.db_for_write(related.field.rel.through, instance=self)
                 opts = related.field.rel.through._meta
                 reverse_field_name = related.field.m2m_reverse_field_name()
                 nullable = opts.get_field(reverse_field_name).null
@@ -622,7 +622,7 @@ class Model(object):
 
         for f in self._meta.many_to_many:
             if f.rel.through:
-                db = router.db_for_write(f.rel.through.__class__, instance=self)
+                db = router.db_for_write(f.rel.through, instance=self)
                 opts = f.rel.through._meta
                 field_name = f.m2m_field_name()
                 nullable = opts.get_field(field_name).null
diff --git a/tests/regressiontests/multiple_database/tests.py b/tests/regressiontests/multiple_database/tests.py
index c0bcedf0aa..052396bd75 100644
--- a/tests/regressiontests/multiple_database/tests.py
+++ b/tests/regressiontests/multiple_database/tests.py
@@ -1739,7 +1739,7 @@ class ModelMetaRouter(object):
         if not hasattr(model, '_meta'):
             raise ValueError
 
-class RouterM2MThroughTestCase(TestCase):
+class RouterModelArgumentTestCase(TestCase):
     multi_db = True
 
     def setUp(self):
@@ -1749,7 +1749,7 @@ class RouterM2MThroughTestCase(TestCase):
     def tearDown(self):
         router.routers = self.old_routers
 
-    def test_m2m_through(self):
+    def test_m2m_collection(self):
         b = Book.objects.create(title="Pro Django",
                                 published=datetime.date(2008, 12, 16))
 
@@ -1760,3 +1760,13 @@ class RouterM2MThroughTestCase(TestCase):
         b.authors.remove(p)
         # test clear
         b.authors.clear()
+        # test setattr
+        b.authors = [p]
+        # Test M2M collection (_collect_sub_objects() in Django <= 1.2.X)
+        b.delete()
+
+    def test_foreignkey_collection(self):
+        person = Person.objects.create(name='Bob')
+        pet = Pet.objects.create(owner=person, name='Wart')
+        # Test related FK collection (_collect_sub_objects() in Django <= 1.2.X)
+        person.delete()