diff --git a/lib/krb5/krb5_mk_req.3 b/lib/krb5/krb5_mk_req.3
index 5bedff6db..70a8e2586 100644
--- a/lib/krb5/krb5_mk_req.3
+++ b/lib/krb5/krb5_mk_req.3
@@ -142,7 +142,39 @@ returns a mutual authentication packet.
 .Pp
 The
 .Nm krb5_rd_req
-\&...
+read the AP_REQ in
+.Fa inbuf
+and verify and extract the content .
+If
+.Fa server
+is specified, that server will be fetched from the
+.Fa keytab
+and used unconditionally.
+If
+.Fa server
+is
+.Dv NULL ,
+the
+.Fa keytab
+will be search for a matching principal.
+.Pp
+The
+.Fa keytab
+argument specifies what keytab to search for receiving principals.
+The arguments
+.Fa ap_req_options
+and
+.Fa ticket
+returns the content.
+.Pp
+When the AS-REQ is a user to user request, neither of
+.Fa keytab
+or
+.Fa principal
+are used, instead
+.Fn krb5_rd_req
+expects the session key to be set in
+.Fa auth_context .
 .Pp
 The
 .Nm krb5_build_ap_req