diff --git a/reference/var/functions/is-resource.xml b/reference/var/functions/is-resource.xml
index c5366ba8b7..33e4680264 100644
--- a/reference/var/functions/is-resource.xml
+++ b/reference/var/functions/is-resource.xml
@@ -64,6 +64,15 @@ if (!is_resource($db_link)) {
    </example>
   </para>
  </refsect1>
+ 
+ <refsect1 role="notes">
+  &reftitle.notes;
+  <note>
+   <para>
+    <function>is_resource</function> is not a strict type-checking method: it will return &false; if <parameter>var</parameter> is a resource variable that has been closed.
+   </para>
+  </note>
+ </refsect1>
 
  <refsect1 role="seealso">
   &reftitle.seealso;