diff --git a/reference/pdo/constants.xml b/reference/pdo/constants.xml
index 8a8fe11802..466060251e 100644
--- a/reference/pdo/constants.xml
+++ b/reference/pdo/constants.xml
@@ -300,7 +300,8 @@
    <listitem>
     <simpara>
      As <constant>PDO::FETCH_INTO</constant> but object is provided as a serialized string.
-     Available since PHP 5.1.0.
+     Available since PHP 5.1.0. Since PHP 5.3.0 the class constructor is never called if this
+     flag is set.
     </simpara>
    </listitem>
   </varlistentry>