diff --git a/reference/var/functions/serialize.xml b/reference/var/functions/serialize.xml
index c546c8f80d..f58c5b800d 100644
--- a/reference/var/functions/serialize.xml
+++ b/reference/var/functions/serialize.xml
@@ -127,7 +127,16 @@ if (!odbc_execute($stmt, $sqldata)) {
   &reftitle.notes;
   <note>
    <para>
-    It is not possible to serialize PHP built-in objects.
+    Note that many built-in PHP objects cannot be serialized. However those with 
+    the ability either implement the <interfacename>Serializable</interface> or the 
+    magic <literal>__sleep</literal> and <literal>__wakeup</literal> methods. If an 
+    internal class doesn't forfill any of those requirements, it cannot reliably be 
+    serialized.
+   </para>
+   <para>
+    There are some historical exceptions to the above rule, where some internal objects 
+    could be serialized without implementing the interface or exposing the methods. Notable 
+    is the <classname>ArrayObject</classname> prior to PHP 5.2.0.
    </para>
   </note>
  </refsect1>