diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 06860e2..6295b18 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -492,6 +492,7 @@
 #define MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_EXT      110  /* 0x6E */
 #define MBEDTLS_SSL_ALERT_MSG_UNRECOGNIZED_NAME    112  /* 0x70 */
 #define MBEDTLS_SSL_ALERT_MSG_UNKNOWN_PSK_IDENTITY 115  /* 0x73 */
+#define MBEDTLS_SSL_ALERT_MSG_CERT_REQUIRED        116  /* 0x74 */
 #define MBEDTLS_SSL_ALERT_MSG_NO_APPLICATION_PROTOCOL 120 /* 0x78 */
 
 #define MBEDTLS_SSL_HS_HELLO_REQUEST            0