diff --git a/lib/bootstrap/bundler.rb b/lib/bootstrap/bundler.rb
index 2672c6e0e36..1e12459bbfc 100644
--- a/lib/bootstrap/bundler.rb
+++ b/lib/bootstrap/bundler.rb
@@ -17,6 +17,7 @@
 
 require "fileutils"
 require "stringio"
+require 'set'
 
 module LogStash
   module Bundler