diff --git a/language/predefined/weakmap/offsetexists.xml b/language/predefined/weakmap/offsetexists.xml
index b5ac8509d04e..da768e92d52b 100644
--- a/language/predefined/weakmap/offsetexists.xml
+++ b/language/predefined/weakmap/offsetexists.xml
@@ -38,6 +38,17 @@
    Returns &true; if the object is contained in the map, &false; otherwise.
   </para>
  </refsect1>
+
+ <refsect1 role="notes">
+  &reftitle.notes;
+  <note>
+   <simpara>
+    Like <function>isset</function>, this method returns &false; if the value
+    associated with <parameter>object</parameter> is &null;, even though the
+    object is still contained in the map.
+   </simpara>
+  </note>
+ </refsect1>
 </refentry>
 <!-- Keep this comment at the end of the file
 Local variables: