diff --git a/tests/xapian_backend.py b/tests/xapian_backend.py
index 303f7a9..3e8fcc3 100644
--- a/tests/xapian_backend.py
+++ b/tests/xapian_backend.py
@@ -84,6 +84,7 @@ class XapianSearchBackendTestCase(TestCase):
     
     def test_update(self):
         self.sb.update(self.msi, self.sample_objs)
+        self.sb.update(self.msi, self.sample_objs) # Duplicates should be updated, not appended -- http://github.com/notanumber/xapian-haystack/issues/#issue/6
 
         self.assertEqual(len(self.xapian_search('')), 3)
         self.assertEqual([dict(doc) for doc in self.xapian_search('')], [{'name': u'david1', 'text': u'Indexed!\n1', 'pub_date': u'2009-02-24T00:00:00', 'id': u'tests.mockmodel.1'}, {'name': u'david2', 'text': u'Indexed!\n2', 'pub_date': u'2009-02-23T00:00:00', 'id': u'tests.mockmodel.2'}, {'name': u'david3', 'text': u'Indexed!\n3', 'pub_date': u'2009-02-22T00:00:00', 'id': u'tests.mockmodel.3'}])
diff --git a/xapian_backend.py b/xapian_backend.py
index 9672887..3225e7d 100644
--- a/xapian_backend.py
+++ b/xapian_backend.py
@@ -158,7 +158,7 @@ class SearchBackend(BaseSearchBackend):
                     (obj._meta.app_label, obj._meta.module_name)
                 )
 
-                database.replace_document(document_id, document)
+                database.replace_document(DOCUMENT_ID_TERM_PREFIX + document_id, document)
 
             database.set_metadata('fields', pickle.dumps(set(fields)))