diff --git a/lib/cudd-rb/interfaces/bdd.rb b/lib/cudd-rb/interfaces/bdd.rb
index <HASH>..<HASH> 100644
--- a/lib/cudd-rb/interfaces/bdd.rb
+++ b/lib/cudd-rb/interfaces/bdd.rb
@@ -14,7 +14,7 @@ module Cudd
         m = self
         pointer.tap do |p|
           p.instance_eval{ @manager = m }
-          p.extend(Cudd::BDD).ref
+          p.extend(Cudd::BDD)
         end
       end
Remove automatic referencing of BDDs.