diff --git a/runfile.js b/runfile.js
index 1c8920f..7e23f4b 100644
--- a/runfile.js
+++ b/runfile.js
@@ -171,7 +171,7 @@ async function build(dist = false) {
  */
 async function optimize() {
     // TODO do not overwrite dev build
-    await exec("uglifyjs out/build.dist.js --source-map --output out/build.js");
+    await exec("uglifyjs out/build.dist.js --source-map --ecma 6 --mangle --keep-classnames --compress --output out/build.js");
 }
 
 /**