diff -r fd487d261169 -r 5036edb025b7 src/Pure/Tools/build.scala
--- a/src/Pure/Tools/build.scala	Sat Apr 04 18:05:37 2020 +0200
+++ b/src/Pure/Tools/build.scala	Sat Apr 04 18:13:05 2020 +0200
@@ -584,7 +584,7 @@
 
     def sleep()
     {
-      try { Thread.sleep(500) }
+      try { Time.seconds(0.5).sleep }
       catch { case Exn.Interrupt() => Exn.Interrupt.impose() }
     }