diff -r 1ce77362598f -r a902f158b4fc src/Pure/Concurrent/future.ML
--- a/src/Pure/Concurrent/future.ML	Tue Jul 20 14:41:13 2010 +0200
+++ b/src/Pure/Concurrent/future.ML	Tue Jul 20 14:44:33 2010 +0200
@@ -409,7 +409,7 @@
 
 fun get_result x =
   (case peek x of
-    NONE => Exn.Exn (SYS_ERROR "unfinished future")
+    NONE => Exn.Exn (Fail "Unfinished future")
   | SOME (exn as Exn.Exn Exn.Interrupt) =>
       (case Exn.flatten_list (Task_Queue.group_status (group_of x)) of
         [] => exn