diff --git a/Jakefile.js b/Jakefile.js
index 595875dfc32..5779d75022f 100644
--- a/Jakefile.js
+++ b/Jakefile.js
@@ -945,7 +945,7 @@ task("generate-code-coverage", ["tests", builtLocalDirectory], function () {
 // Browser tests
 var nodeServerOutFile = "tests/webTestServer.js";
 var nodeServerInFile = "tests/webTestServer.ts";
-compileFile(nodeServerOutFile, [nodeServerInFile], [builtLocalDirectory, tscFile], [], /*useBuiltCompiler:*/ true, { noOutFile: true });
+compileFile(nodeServerOutFile, [nodeServerInFile], [builtLocalDirectory, tscFile], [], /*useBuiltCompiler:*/ true, { noOutFile: true, lib: "es6" });
 
 desc("Runs browserify on run.js to produce a file suitable for running tests in the browser");
 task("browserify", ["tests", builtLocalDirectory, nodeServerOutFile], function() {