diff --git a/include/openssl/tls1.h b/include/openssl/tls1.h
index 384d102..f7766f2 100644
--- a/include/openssl/tls1.h
+++ b/include/openssl/tls1.h
@@ -244,6 +244,9 @@
 // This is not an IANA defined extension number
 #define TLSEXT_TYPE_channel_id 30032
 
+// This is not an IANA defined extension number
+#define TLSEXT_TYPE_pq_experiment_signal 54538
+
 // status request value from RFC 3546
 #define TLSEXT_STATUSTYPE_nothing (-1)
 #define TLSEXT_STATUSTYPE_ocsp 1