diff --git a/docs/refguide.xml b/docs/refguide.xml
index 91d7faf89..9500fb488 100644
--- a/docs/refguide.xml
+++ b/docs/refguide.xml
@@ -673,9 +673,11 @@ you would expect.</para>
           request behavior.</para>
 
           <para>While echo request is the standard ICMP ping query,
-          Nmap does not stop there.  The ICMP standard (<ulink
-          role="hidepdf" url="http://www.rfc-editor.org/rfc/rfc792.txt">RFC
-          792</ulink>) also specifies timestamp request, information
+          Nmap does not stop there.  The ICMP standard
+          <ulink role="hidepdf" url="http://www.rfc-editor.org/rfc/rfc792.txt">RFC 792</ulink><indexterm><primary>RFC 792</primary></indexterm>
+          and
+          <ulink role="hidepdf" url="http://www.rfc-editor.org/rfc/rfc950.txt">RFC 950</ulink><indexterm><primary>RFC 950</primary></indexterm>
+          also specify timestamp request, information
           request, and address mask request packets as codes 13, 15,
           and 17, respectively.  While the ostensible purpose for
           these queries is to learn information such as address masks