diff --git a/mongoengine/dereference.py b/mongoengine/dereference.py
index 0f60c2f5..cc710f4d 100644
--- a/mongoengine/dereference.py
+++ b/mongoengine/dereference.py
@@ -220,7 +220,7 @@ class DeReference(object):
                     elif isinstance(v, (dict, SON)) and '_ref' in v:
                         data[k]._data[field_name] = self.object_map.get(v['_ref'].id, v)
                     elif isinstance(v, dict) and depth <= self.max_depth:
-                        item_name = "%s.%s.%s" % (name, k, field_name)
+                        item_name = "{0}.{1}.{2}".format(name, k, field_name)
                         data[k]._data[field_name] = self._attach_objects(v, depth, instance=instance, name=item_name)
                     elif isinstance(v, (list, tuple)) and depth <= self.max_depth:
                         data[k]._data[field_name] = self._attach_objects(v, depth, instance=instance, name=name)