diff --git a/scripts/gulpfiles/appengine_tasks.js b/scripts/gulpfiles/appengine_tasks.js
index e07b9f60f..e8114587a 100644
--- a/scripts/gulpfiles/appengine_tasks.js
+++ b/scripts/gulpfiles/appengine_tasks.js
@@ -47,8 +47,8 @@ function copyStaticSrc(done) {
  */
 function copyAppengineSrc() {
   const appengineSrc = [
-      path.join(demoStaticTmpDir, 'appengine/**/*'),
-      path.join(demoStaticTmpDir, 'appengine/.gcloudignore'),
+      `${demoStaticTmpDir}/appengine/**/*`,
+      `${demoStaticTmpDir}/appengine/.gcloudignore`,
   ];
   return gulp.src(appengineSrc).pipe(gulp.dest(demoTmpDir));
 }