diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 901e26d..da8b6b3 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -1707,6 +1707,22 @@
 #define MBEDTLS_SSL_PROTO_TLS1_2
 
 /**
+ * \def MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL
+ *
+ * This is an experimental macro used to selectively enable parts
+ * of the code that solely contribute to the ongoing development of
+ * a prototype implementation for TLS 1.3 and DTLS 1.3 but aren't
+ * used otherwise.
+ *
+ * \warning Features under the control of this macro are experimental
+ *          and don't come with any stability guarantees.
+ *
+ * Uncomment this macro to enable experimental and partial
+ * functionality specific to TLS 1.3.
+ */
+#define MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL
+
+/**
  * \def MBEDTLS_SSL_PROTO_DTLS
  *
  * Enable support for DTLS (all available versions).