diff -r d83e7e444b43 -r 7202e12cb324 src/Pure/System/scala.scala
--- a/src/Pure/System/scala.scala	Sun May 16 13:14:16 2021 +0200
+++ b/src/Pure/System/scala.scala	Sun May 16 13:34:27 2021 +0200
@@ -69,7 +69,7 @@
           case _ => error("Malformed argument: " + quote(seconds))
         }
       val t0 = Time.now()
-      t.sleep
+      t.sleep()
       val t1 = Time.now()
       (t1 - t0).toString
     }