diff -up openssl-3.0.0-alpha16/ssl/s3_msg.c.shut-down openssl-3.0.0-alpha16/ssl/s3_msg.c
--- openssl-3.0.0-alpha16/ssl/s3_msg.c.shut-down	2021-05-17 11:11:11.050702699 +0200
+++ openssl-3.0.0-alpha16/ssl/s3_msg.c	2021-05-17 11:12:37.741526784 +0200
@@ -52,6 +52,8 @@ int ssl3_send_alert(SSL *s, int level, i
                                           * protocol_version alerts */
     if (desc < 0)
         return -1;
+    if (s->shutdown & SSL_SENT_SHUTDOWN && desc != SSL_AD_CLOSE_NOTIFY)
+        return -1;
     /* If a fatal one, remove from cache */
     if ((level == SSL3_AL_FATAL) && (s->session != NULL))
         SSL_CTX_remove_session(s->session_ctx, s->session);