diff --git a/epan/dissectors/packet-sdp.c b/epan/dissectors/packet-sdp.c
index f3b19bd344..03ca9c8dea 100644
--- a/epan/dissectors/packet-sdp.c
+++ b/epan/dissectors/packet-sdp.c
@@ -23,6 +23,7 @@
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
+ * Ref http://www.ietf.org/rfc/rfc4566.txt?number=4566
  */
 
 #include "config.h"