src/HOL/Tools/datatype_package.ML

--- a/src/HOL/Tools/datatype_package.ML	Fri Aug 24 14:14:18 2007 +0200
+++ b/src/HOL/Tools/datatype_package.ML	Fri Aug 24 14:14:20 2007 +0200
@@ -567,6 +567,7 @@
         thy
         |> Class.prove_instance_arity (Class.intro_classes_tac [])
             [(tyco, replicate n HOLogic.typeS, [HOLogic.class_size])] []
+        |> snd
       end
 
     val thy2' = thy