diff -r 31e75ad9ae17 -r 9dd0a2f83429 src/Tools/quickcheck.ML
--- a/src/Tools/quickcheck.ML	Tue Sep 29 14:59:24 2009 +0200
+++ b/src/Tools/quickcheck.ML	Tue Sep 29 16:24:36 2009 +0200
@@ -6,8 +6,8 @@
 
 signature QUICKCHECK =
 sig
-  val auto: bool ref
-  val auto_time_limit: int ref
+  val auto: bool Unsynchronized.ref
+  val auto_time_limit: int Unsynchronized.ref
   val test_term: Proof.context -> bool -> string option -> int -> int -> term ->
     (string * term) list option
   val add_generator: string * (Proof.context -> term -> int -> term list option) -> theory -> theory
@@ -19,8 +19,8 @@
 
 (* preferences *)
 
-val auto = ref false;
-val auto_time_limit = ref 2500;
+val auto = Unsynchronized.ref false;
+val auto_time_limit = Unsynchronized.ref 2500;
 
 val _ =
   ProofGeneralPgip.add_preference Preferences.category_tracing