diff --git a/lib/roby.rb b/lib/roby.rb
index 40787b3a4..2b39a3aae 100644
--- a/lib/roby.rb
+++ b/lib/roby.rb
@@ -32,6 +32,7 @@ class Task < PlanObject; end
 require 'utilrb/module/attr_enumerable'
 require 'utilrb/module/attr_predicate'
 require 'utilrb/module/include'
+require 'utilrb/module/is_singleton'
 require 'utilrb/kernel/arity'
 require 'utilrb/kernel/swap'
 require 'utilrb/exception/full_message'