diff --git a/src/harness/virtualFileSystemWithWatch.ts b/src/harness/virtualFileSystemWithWatch.ts
index 57fa33a84c2..8c241772227 100644
--- a/src/harness/virtualFileSystemWithWatch.ts
+++ b/src/harness/virtualFileSystemWithWatch.ts
@@ -4,6 +4,8 @@ namespace ts.TestFSWithWatch {
         content: `/// <reference no-default-lib="true"/>
 interface Boolean {}
 interface Function {}
+interface CallableFunction {}
+interface NewableFunction {}
 interface IArguments {}
 interface Number { toExponential: any; }
 interface Object {}