diff --git a/reference/oauth/oauthprovider/setparam.xml b/reference/oauth/oauthprovider/setparam.xml
index 31d8cfb3c6..d2ef623264 100644
--- a/reference/oauth/oauthprovider/setparam.xml
+++ b/reference/oauth/oauthprovider/setparam.xml
@@ -39,6 +39,10 @@
      <para>
       The optional parameter value.
      </para>
+     <para>
+      To exclude a parameter from signature verification, set
+      its value to &null;.
+     </para>
     </listitem>
    </varlistentry>
   </variablelist>