diff --git a/docs/refguide.xml b/docs/refguide.xml
index 549829170..00978c834 100644
--- a/docs/refguide.xml
+++ b/docs/refguide.xml
@@ -450,6 +450,10 @@ you would expect.</para>
            could be missed when the firewall drops probes or their
            responses.</para>
 
+           <para>In previous releases of Nmap, <option>-sn</option> was
+           known as
+           <option>-sP</option>.<indexterm><primary><option>-sP</option></primary><seealso><option>-sn</option></seealso></indexterm></para>
+
         </listitem>
       </varlistentry>
 
@@ -481,7 +485,12 @@ you would expect.</para>
           <para>For machines on a local ethernet network, ARP
           scanning will still be performed (unless
           <option>--send-ip</option> is specified) because Nmap needs
-          MAC addresses to further scan target hosts.  This option flag used to be <option>P0</option> (uses zero), but was renamed to avoid confusion with protocol ping's <option>PO</option> (uses the letter O) flag.</para>
+          MAC addresses to further scan target hosts. In previous
+          versions of Nmap, <option>-Pn</option> was
+          <option>-P0</option><indexterm><primary><option>-P0</option></primary><seealso><option>-Pn</option></seealso></indexterm>
+          and
+          <option>-PN</option>.<indexterm><primary><option>-PN</option></primary><seealso><option>-Pn</option></seealso></indexterm>
+          </para>
         </listitem>
       </varlistentry>