diff --git a/util/TLSProxy/ClientHello.pm b/util/TLSProxy/ClientHello.pm
index bd03183aabb6eed69d351a0be4a9795f4b95dfef..c6f3c3fe04c74fa48352f02ae21677d536a20ce7 100644
--- a/util/TLSProxy/ClientHello.pm
+++ b/util/TLSProxy/ClientHello.pm
@@ -59,6 +59,7 @@ use parent 'TLSProxy::Message';
 
 use constant {
     EXT_ENCRYPT_THEN_MAC => 22,
+    EXT_EXTENDED_MASTER_SECRET => 23,
     EXT_SESSION_TICKET => 35
 };