diff --git a/docs/changelog.rst b/docs/changelog.rst
index c2a5cb47..d7c7761f 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -2,6 +2,10 @@
 Changelog
 =========
 
+Changes in 0.7.X
+================
+- Update index spec generation so its not destructive (MongoEngine/mongoengine#113)
+
 Changes in 0.7.1
 =================
 - Fixed index spec inheritance (MongoEngine/mongoengine#111)
diff --git a/mongoengine/queryset.py b/mongoengine/queryset.py
index b020209b..6f913fc7 100644
--- a/mongoengine/queryset.py
+++ b/mongoengine/queryset.py
@@ -398,6 +398,7 @@ class QuerySet(object):
             or a **-** to determine the index ordering
         """
         index_spec = QuerySet._build_index_spec(self._document, key_or_list)
+        index_spec = index_spec.copy()
         fields = index_spec.pop('fields')
         index_spec['drop_dups'] = drop_dups
         index_spec['background'] = background
@@ -472,7 +473,9 @@ class QuerySet(object):
 
         # Ensure document-defined indexes are created
         if self._document._meta['index_specs']:
-            for spec in self._document._meta['index_specs']:
+            index_spec = self._document._meta['index_specs']
+            for spec in index_spec:
+                spec = spec.copy()
                 fields = spec.pop('fields')
                 types_indexed = types_indexed or includes_types(fields)
                 opts = index_opts.copy()
diff --git a/tests/test_document.py b/tests/test_document.py
index 976a2731..9637bfeb 100644
--- a/tests/test_document.py
+++ b/tests/test_document.py
@@ -688,6 +688,25 @@ class DocumentTest(unittest.TestCase):
 
         self.assertEqual(A._meta['index_specs'], B._meta['index_specs'])
 
+    def test_build_index_spec_is_not_destructive(self):
+
+        class MyDoc(Document):
+            keywords = StringField()
+
+            meta = {
+                'indexes': ['keywords'],
+                'allow_inheritance': False
+            }
+
+        self.assertEqual(MyDoc._meta['index_specs'],
+                         [{'fields': [('keywords', 1)]}])
+
+        # Force index creation
+        MyDoc.objects._ensure_indexes()
+
+        self.assertEqual(MyDoc._meta['index_specs'],
+                        [{'fields': [('keywords', 1)]}])
+
     def test_db_field_load(self):
         """Ensure we load data correctly
         """