diff -r 9247996782c9 -r 4535a45182d5 src/Pure/Concurrent/synchronized.ML
--- a/src/Pure/Concurrent/synchronized.ML	Sun Jul 22 13:00:38 2018 +0200
+++ b/src/Pure/Concurrent/synchronized.ML	Sun Jul 22 14:01:52 2018 +0200
@@ -54,7 +54,7 @@
           Immutable _ => immutable_fail name
         | Mutable _ =>
             Thread_Attributes.uninterruptible (fn _ => fn () =>
-             (state := Immutable x; (* FIXME RunCall.clearMutableBit state; *)
+             (state := Immutable x; RunCall.clearMutableBit state;
                ConditionVar.broadcast cond)) ())));