diff --git a/index.js b/index.js
index d789a83..f9fd05c 100644
--- a/index.js
+++ b/index.js
@@ -9,7 +9,7 @@ module.exports = function vueify (file, options) {
   compiler.loadConfig()
   compiler.applyConfig(options)
   compiler.applyConfig({
-    sourceMap: options._flags.debug
+    sourceMap: !!options._flags && options._flags.debug
   })
 
   var data = ''