diff --git a/Library/Homebrew/download_strategy.rb b/Library/Homebrew/download_strategy.rb
index 0c8de9b494..4ff56f290d 100644
--- a/Library/Homebrew/download_strategy.rb
+++ b/Library/Homebrew/download_strategy.rb
@@ -5,6 +5,7 @@ require "time"
 require "unpack_strategy"
 require "lazy_object"
 require "cgi"
+require "lock_file"
 
 require "mechanize/version"
 require "mechanize/http/content_disposition_parser"