diff --git a/library/ssl_tls13_server.c b/library/ssl_tls13_server.c
index d68403f..bf863d5 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -740,7 +740,9 @@
 
     MBEDTLS_SSL_PROC_CHK_NEG( ssl_tls13_parse_client_hello( ssl, buf,
                                                             buf + buflen ) );
-    parse_client_hello_ret = ret;
+    parse_client_hello_ret = ret; /* store return reason of parse_client_hello
+                                     without error. on error, this statment will
+                                     not be called.*/
 
     MBEDTLS_SSL_PROC_CHK( ssl_tls13_postprocess_client_hello( ssl ) );