diff --git a/lib/perpetuity/mongodb/serializer.rb b/lib/perpetuity/mongodb/serializer.rb
index <HASH>..<HASH> 100644
--- a/lib/perpetuity/mongodb/serializer.rb
+++ b/lib/perpetuity/mongodb/serializer.rb
@@ -1,4 +1,5 @@
 require 'perpetuity/data_injectable'
+require 'perpetuity/reference'
 
 module Perpetuity
   class MongoDB
Require Reference class in Serializer