diff --git a/engine/lib/coplan.rb b/engine/lib/coplan.rb
index 8b5707b6..be72b13d 100644
--- a/engine/lib/coplan.rb
+++ b/engine/lib/coplan.rb
@@ -1,3 +1,4 @@
+require "commonmarker"
 require "coplan/configuration"
 require "coplan/engine"