diff -r 54f06ba192ef -r ee7fe4230642 src/Pure/Concurrent/future.ML
--- a/src/Pure/Concurrent/future.ML	Wed Jan 16 11:31:08 2013 +0100
+++ b/src/Pure/Concurrent/future.ML	Wed Jan 16 16:26:36 2013 +0100
@@ -439,7 +439,7 @@
   let
     val res =
       (case raw_res of
-        Exn.Exn exn => Exn.Exn (Par_Exn.set_serial exn)
+        Exn.Exn exn => Exn.Exn (Par_Exn.identify [] exn)
       | _ => raw_res);
     val _ = Single_Assignment.assign result res
       handle exn as Fail _ =>