diff --git a/docs/refguide.xml b/docs/refguide.xml
index 5bdba4e4a..f9e667b54 100644
--- a/docs/refguide.xml
+++ b/docs/refguide.xml
@@ -660,11 +660,11 @@ you would expect.</para>
           IP packets for ICMP (protocol 1), IGMP (protocol 2), and
           IP-in-IP (protocol 4).  The default protocols can be
           configured at compile-time by changing DEFAULT_PROTO_PROBE_PORTS
-          in <filename>nmap.h</filename>.  Note that for the ICMP and IGMP,
-          the packets are sent with the additional headers while other
-          protocols are sent with no additional data beyond the IP
-          header (unless the <option>--data-length</option> option is
-          specified).</para>
+          in <filename>nmap.h</filename>.  Note that for the ICMP, IGMP,
+          TCP (protocol 6), and UDP (protocol 17), the packets are sent
+          with the additional headers while other protocols are sent with
+          no additional data beyond the IP header (unless the
+          <option>--data-length</option> option is specified).</para>
 
           <para>This host discovery method looks for responses in the
           same protocol as the probes, or ICMP Protocol Unreachable