diff --git a/nprogress/NProgress-tests.ts b/nprogress/NProgress-tests.ts
index 24613e0be..d7ad68b39 100644
--- a/nprogress/NProgress-tests.ts
+++ b/nprogress/NProgress-tests.ts
@@ -1,3 +1,5 @@
+///<reference path="./NProgress.d.ts"/>
+
 function test_basics() {
     NProgress.start();
     NProgress.inc();