diff --git a/config/environments/production.rb b/config/environments/production.rb
index 219f7fc3..a3844af3 100644
--- a/config/environments/production.rb
+++ b/config/environments/production.rb
@@ -26,7 +26,7 @@ Mapknitter::Application.configure do
   config.serve_static_files = ENV['RAILS_SERVE_STATIC_FILES'].present?
 
   # Compress JavaScripts and CSS.
-  config.assets.js_compressor = :uglifier
+  config.assets.js_compressor = Uglifier.new(harmony: true)
   # config.assets.css_compressor = :sass
 
   # Do not fallback to assets pipeline if a precompiled asset is missed.