diff --git a/include/openssl/tls1.h b/include/openssl/tls1.h
index 4b25806..bb9a816 100644
--- a/include/openssl/tls1.h
+++ b/include/openssl/tls1.h
@@ -205,9 +205,15 @@
 // ExtensionType value from draft-ietf-tokbind-negotiation-10
 #define TLSEXT_TYPE_token_binding 24
 
-// ExtensionType value from draft-ietf-quic-tls
+// ExtensionType value from draft-ietf-quic-tls. Note that this collides with
+// TLS-LTS and, based on scans, something else too. Since it's QUIC-only, that
+// shouldn't be a problem in practice.
 #define TLSEXT_TYPE_quic_transport_parameters 26
 
+// ExtensionType value assigned to
+// https://tools.ietf.org/html/draft-ietf-tls-certificate-compression-03
+#define TLSEXT_TYPE_cert_compression 27
+
 // ExtensionType value from RFC4507
 #define TLSEXT_TYPE_session_ticket 35