diff --git a/tests/xapian_tests/tests/test_xapian_backend.py b/tests/xapian_tests/tests/test_xapian_backend.py
index a12296c..58334d9 100644
--- a/tests/xapian_tests/tests/test_xapian_backend.py
+++ b/tests/xapian_tests/tests/test_xapian_backend.py
@@ -12,7 +12,7 @@ from django.test import TestCase
 
 from haystack import connections, reset_search_queries
 from haystack import indexes
-from haystack.backends.xapian_backend import _marshal_value
+from haystack.backends.xapian_backend import InvalidIndexError, _marshal_value
 from haystack.models import SearchResult
 from haystack.query import SearchQuerySet, SQ
 from haystack.utils.loading import UnifiedIndex
@@ -454,6 +454,24 @@ class XapianSearchBackendTestCase(HaystackBackendTestCase, TestCase):
         self.assertEqual(str(self.backend.parse_query('popularity:25.5..100.0')),
                          b'Xapian::Query(VALUE_RANGE 7 \xb2` \xba@)')
 
+    def test_more_like_this_with_unindexed_model(self):
+        """
+        Tests that more_like_this raises an error when it is called
+         with an unindexed model and if silently_fail is True.
+         Also tests the other way around.
+        """
+        mock = XapianMockModel()
+        mock.id = 10
+        mock.author = 'david10'
+
+        try:
+            self.assertEqual(self.backend.more_like_this(mock)['results'], [])
+        except InvalidIndexError:
+            self.fail("InvalidIndexError raised when silently_fail is True")
+
+        self.backend.silently_fail = False
+        self.assertRaises(InvalidIndexError, self.backend.more_like_this, mock)
+
 
 class LiveXapianMockSearchIndex(indexes.SearchIndex):
     text = indexes.CharField(document=True, use_template=True)
diff --git a/xapian_backend.py b/xapian_backend.py
index cf6ad0e..6ed71c4 100755
--- a/xapian_backend.py
+++ b/xapian_backend.py
@@ -530,9 +530,18 @@ class XapianSearchBackend(BaseSearchBackend):
         if not end_offset:
             end_offset = database.get_doccount()
 
+        match = None
         for match in self._get_enquire_mset(database, enquire, 0, end_offset):
             rset.add_document(match.docid)
 
+        if match is None:
+            if not self.silently_fail:
+                raise InvalidIndexError('Instance %s with id "%d" not indexed' %
+                                        (get_identifier(model_instance), model_instance.id))
+            else:
+                return {'results': [],
+                        'hits': 0}
+
         query = xapian.Query(
             xapian.Query.OP_ELITE_SET,
             [expand.term for expand in enquire.get_eset(match.document.termlist_count(), rset, XHExpandDecider())],