diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 7bb5f9f..c11810d 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -5205,10 +5205,15 @@
 
     if( ret != 0 )
     {
+        /* handshake_step return error. And it is same
+         * with alert_reason.
+         */
         int alert_ret;
         alert_ret = mbedtls_ssl_handle_pending_alert( ssl );
         if( alert_ret != 0 )
         {
+            /* If success send, ret == alert_ret.
+             */
             ret = alert_ret;
             goto cleanup;
         }