src/Pure/Concurrent/counter.scala

--- a/src/Pure/Concurrent/counter.scala	Sat Jan 09 22:41:08 2021 +0100
+++ b/src/Pure/Concurrent/counter.scala	Sun Jan 10 13:04:29 2021 +0100
@@ -20,7 +20,7 @@
   private var count: Counter.ID = 0
 
   def apply(): Counter.ID = synchronized {
-    require(count > java.lang.Long.MIN_VALUE)
+    require(count > java.lang.Long.MIN_VALUE, "counter overflow")
     count -= 1
     count
   }