diff --git a/library/ssl_tls13_server.c b/library/ssl_tls13_server.c
index 52d2db6e7..3baff36e7 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -1925,9 +1925,9 @@ static int ssl_tls13_process_client_hello(mbedtls_ssl_context *ssl)
             MBEDTLS_SSL_DEBUG_MSG(
                 1, ("TLS 1.2 not supported."));
             MBEDTLS_SSL_PEND_FATAL_ALERT(
-                MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER,
-                MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER);
-            return MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER;
+                MBEDTLS_SSL_ALERT_MSG_PROTOCOL_VERSION,
+                MBEDTLS_ERR_SSL_BAD_PROTOCOL_VERSION);
+            return MBEDTLS_ERR_SSL_BAD_PROTOCOL_VERSION;
         }
         ssl->keep_current_message = 1;
         ssl->tls_version = MBEDTLS_SSL_VERSION_TLS1_2;