diff --git a/language/types/boolean.xml b/language/types/boolean.xml
index 0b196a2f4396..2ca481eb3834 100644
--- a/language/types/boolean.xml
+++ b/language/types/boolean.xml
@@ -114,7 +114,9 @@ if ($show_separators) {
     <simpara>
      Internal objects that overload their casting behaviour to bool.
      For example: <link linkend="ref.simplexml">SimpleXML</link> objects
-     created from empty elements without attributes.
+     created from empty elements without attributes, or
+     <classname>GMP</classname> objects representing the value
+     <literal>0</literal>.
     </simpara>
    </listitem>
   </itemizedlist>