diff --git a/concurrent/Summing4.java b/concurrent/Summing4.java
index 1bbeb6be..27353141 100644
--- a/concurrent/Summing4.java
+++ b/concurrent/Summing4.java
@@ -2,6 +2,7 @@
 // (c)2017 MindView LLC: see Copyright.txt
 // We make no guarantees that this code is fit for any purpose.
 // Visit http://OnJava8.com for more book information.
+// {ValidateByHand} // CI has trouble
 import java.util.*;
 
 public class Summing4 {