diff --git a/reference/var/functions/isset.xml b/reference/var/functions/isset.xml
index e4c296dcc2..81c70b7add 100644
--- a/reference/var/functions/isset.xml
+++ b/reference/var/functions/isset.xml
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="iso-8859-1"?>
-<!-- $Revision: 1.6 $ -->
+<!-- $Revision: 1.7 $ -->
 <!-- splitted from ./en/functions/var.xml, last change in rev 1.2 -->
   <refentry id="function.isset">
    <refnamediv>
@@ -33,7 +33,9 @@
      <title>Warning</title>
      <para>
       <function>isset</function> only works with variables as passing anything
-      else will result in a parse error.
+      else will result in a parse error.  For checking if 
+      <link linkend="language.constants">constants</link> are set use the 
+      <function>defined</function> function.
      </para>
     </note>
     <para>
@@ -95,8 +97,10 @@ var_dump( array_key_exists('hello', $a) ); // TRUE
     </para>
     <simpara>
      See also <function>empty</function>,
-     <function>unset</function>, and 
-     <function>array_key_exists</function>.
+     <function>unset</function>, <function>defined</function>,
+     <function>array_key_exists</function> and the error control 
+     <link linkend="language.operators.errorcontrol">@</link>
+     operator.
     </simpara>
    </refsect1>
   </refentry>