diff --git a/lib/foreman/engine.rb b/lib/foreman/engine.rb
index 6047028..97b2dce 100644
--- a/lib/foreman/engine.rb
+++ b/lib/foreman/engine.rb
@@ -7,6 +7,7 @@ require "tempfile"
 require "timeout"
 require "term/ansicolor"
 require "fileutils"
+require "thread"
 
 class Foreman::Engine