diff -r ef876972fdc1 -r 0baa8bbd355a src/Pure/Thy/thy_load.ML
--- a/src/Pure/Thy/thy_load.ML	Wed Aug 10 15:17:24 2011 +0200
+++ b/src/Pure/Thy/thy_load.ML	Wed Aug 10 16:05:14 2011 +0200
@@ -189,7 +189,7 @@
 
     val present =
       singleton (Future.cond_forks {name = "Outer_Syntax.present:" ^ name, group = NONE,
-        deps = map Future.task_of results, pri = 0})
+        deps = map Future.task_of results, pri = 0, interrupts = true})
       (fn () =>
         Thy_Output.present_thy (#1 lexs) Keyword.command_tags
           (Outer_Syntax.is_markup outer_syntax)