diff --git a/src/compiler/tsc.ts b/src/compiler/tsc.ts
index 69d54250aac..1c8a696dd0d 100644
--- a/src/compiler/tsc.ts
+++ b/src/compiler/tsc.ts
@@ -193,7 +193,7 @@ module ts {
 
         return {
             getSourceFile: getSourceFile,
-            getDefaultLibFilename: (options) => combinePaths(getDirectoryPath(normalizePath(sys.getExecutingFilePath())), options.target === ScriptTarget.ES6 ? "lib.es6.d.ts" : "lib.d.ts"),
+            getDefaultLibFilename: options => combinePaths(getDirectoryPath(normalizePath(sys.getExecutingFilePath())), options.target === ScriptTarget.ES6 ? "lib.es6.d.ts" : "lib.d.ts"),
             writeFile: writeFile,
             getCurrentDirectory: () => currentDirectory || (currentDirectory = sys.getCurrentDirectory()),
             useCaseSensitiveFileNames: () => sys.useCaseSensitiveFileNames,
diff --git a/src/harness/projectsRunner.ts b/src/harness/projectsRunner.ts
index 35efbffbd68..592dce5c2ea 100644
--- a/src/harness/projectsRunner.ts
+++ b/src/harness/projectsRunner.ts
@@ -184,7 +184,7 @@ class ProjectRunner extends RunnerBase {
             function createCompilerHost(): ts.CompilerHost {
                 return {
                     getSourceFile: getSourceFile,
-                    getDefaultLibFilename: () => "lib.d.ts",
+                    getDefaultLibFilename: options => options.target === ts.ScriptTarget.ES6 ? "lib.es6.d.ts" : "lib.d.ts",
                     writeFile: writeFile,
                     getCurrentDirectory: getCurrentDirectory,
                     getCanonicalFileName: Harness.Compiler.getCanonicalFileName,