diff --git a/src/chapters/duo-auth.xml b/src/chapters/duo-auth.xml
index d92c469..680e104 100644
--- a/src/chapters/duo-auth.xml
+++ b/src/chapters/duo-auth.xml
@@ -167,7 +167,7 @@
                             been generated by Duo when you added Guacamole as an "Web SDK"
                             application, and can be found within the application details in the
                             "Secret key" field. <emphasis>This value is required and must be EXACTLY
-                                20 characters.</emphasis></para>
+                                40 characters.</emphasis></para>
                     </listitem>
                 </varlistentry>
             </variablelist>