diff -r 92c6ddca552e -r 17100f4ce0b5 src/HOL/Tools/Predicate_Compile/code_prolog.ML
--- a/src/HOL/Tools/Predicate_Compile/code_prolog.ML	Sun Dec 04 18:30:57 2011 +0100
+++ b/src/HOL/Tools/Predicate_Compile/code_prolog.ML	Sun Dec 04 20:05:08 2011 +0100
@@ -1039,7 +1039,7 @@
       | _ => NONE
   in
     Quickcheck.Result
-      {counterexample = Option.map ((curry (op ~~)) (Term.add_free_names t [])) counterexample,
+      {counterexample = Option.map (pair true o curry (op ~~) (Term.add_free_names t [])) counterexample,
        evaluation_terms = Option.map (K []) counterexample, timings = [], reports = []}
   end;