diff --git a/backbone-relational/backbone-relational-tests.ts b/backbone-relational/backbone-relational-tests.ts
index acc31417b..606bfdf19 100644
--- a/backbone-relational/backbone-relational-tests.ts
+++ b/backbone-relational/backbone-relational-tests.ts
@@ -1,4 +1,5 @@
 /// <reference path="../backbone/backbone.d.ts" />
+/// <reference path="../underscore/underscore.d.ts" />
 /// <reference path="backbone-relational.d.ts" />
 
 class House extends Backbone.RelationalModel {