diff --git a/lib/vagrant/action/box/download.rb b/lib/vagrant/action/box/download.rb
index e132cec10..19b8751ca 100644
--- a/lib/vagrant/action/box/download.rb
+++ b/lib/vagrant/action/box/download.rb
@@ -13,8 +13,7 @@ module Vagrant
           @app = app
           @env = env
           @env["download.classes"] ||= []
-          @env["download.classes"] << [Downloaders::HTTP, Downloaders::File]
-          @env["download.classes"].flatten!
+          @env["download.classes"] += [Downloaders::HTTP, Downloaders::File]
         end
 
         def call(env)