diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index 111343e08ff..a01f3a4c5b2 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -180,7 +180,7 @@ namespace ts {
 
     function getEffectiveTypeRoots(options: CompilerOptions, host: ModuleResolutionHost) {
         return options.typeRoots ||
-            defaultTypeRoots.map(d => combinePaths(options.configFilePath ? getDirectoryPath(options.configFilePath) : host.getCurrentDirectory(), d));
+            map(defaultTypeRoots, d => combinePaths(options.configFilePath ? getDirectoryPath(options.configFilePath) : host.getCurrentDirectory(), d));
     }
 
     /**