diff --git a/language/oop5/magic.xml b/language/oop5/magic.xml
index 626a4e0057..b806632e7b 100644
--- a/language/oop5/magic.xml
+++ b/language/oop5/magic.xml
@@ -41,8 +41,16 @@
     and is supposed to return an array with the names of all variables
     of that object that should be serialized.
     If the method doesn't return anything then &null; is serialized and
-    E_NOTICE is issued.
+    <constant>E_NOTICE</constant> is issued.
    </para>
+   <note>
+    <para>
+     It is not possible for <literal>__sleep</literal> to return names of
+     private properties in parent classes. Doing this will result in an
+     <constant>E_NOTICE</constant> level error. Instead you may use the
+     <classname>Serializable</classname> interface.
+    </para>
+   </note>
    <para>
     The intended use of <literal>__sleep</literal> is to commit pending
     data or perform similar cleanup tasks. Also, the function is