diff --git a/reference/classobj/functions/get-parent-class.xml b/reference/classobj/functions/get-parent-class.xml
index 66225840ba..7243dd8f21 100644
--- a/reference/classobj/functions/get-parent-class.xml
+++ b/reference/classobj/functions/get-parent-class.xml
@@ -8,7 +8,7 @@
  <refsect1 role="description">
   &reftitle.description;
   <methodsynopsis>
-   <type>string</type><methodname>get_parent_class</methodname>
+   <type class="union"><type>string</type><type>false</type></type><methodname>get_parent_class</methodname>
    <methodparam choice="opt"><type class="union"><type>object</type><type>string</type></type><parameter>object_or_class</parameter></methodparam>
   </methodsynopsis>
   <para>