diff --git a/bin/named/named.docbook b/bin/named/named.docbook
index 0ea469d357..788c18fcb8 100644
--- a/bin/named/named.docbook
+++ b/bin/named/named.docbook
@@ -307,8 +307,9 @@
             worker threads to listen for incoming UDP packets on each
             address.  If not specified, <command>named</command> will
             calculate a default value based on the number of detected
-            CPUs: 1 for 1 CPU, 2 for 2-4 CPUs, and the number of
-            detected CPUs divided by 2 for values higher than 4.
+            CPUs: 1 for 1 CPU, and the number of detected CPUs
+            minus one for machines with more than 1 CPU. This cannot
+            be increased to a value higher than the number of CPUs.
             If <option>-n</option> has been set to a higher value than
             the number of detected CPUs, then <option>-U</option> may
             be increased as high as that value, but no higher.