--- a/src/Pure/Concurrent/cache.ML	Thu Jun 22 14:27:13 2017 +0200
+++ b/src/Pure/Concurrent/cache.ML	Thu Jun 22 15:20:32 2017 +0200
@@ -23,7 +23,7 @@
           (case lookup tab x of
             SOME y => (y, tab)
           | NONE =>
-              let val y = Lazy.lazy (fn () => f x)
+              let val y = Lazy.lazy_name "cache" (fn () => f x)
               in (y, update (x, y) tab) end))
       |> Lazy.force;
   in apply end;