diff --git a/g10/mainproc.c b/g10/mainproc.c
index f7b7c6b2c..9f02b1555 100644
--- a/g10/mainproc.c
+++ b/g10/mainproc.c
@@ -607,6 +607,22 @@ proc_encrypted (CTX c, PACKET *pkt)
 
   if (result == -1)
     ;
+  else if (!result
+           && !opt.ignore_mdc_error
+           && !pkt->pkt.encrypted->mdc_method
+           && openpgp_cipher_get_algo_blklen (c->dek->algo) != 8
+           && c->dek->algo != CIPHER_ALGO_TWOFISH)
+    {
+      /* The message has been decrypted but has no MDC despite that a
+         modern cipher (blocklength != 64 bit, except for Twofish) is
+         used and the option to ignore MDC errors is not used: To
+         avoid attacks changing an MDC message to a non-MDC message,
+         we fail here.  */
+      log_error (_("WARNING: message was not integrity protected\n"));
+      if (opt.verbose > 1)
+        log_info ("decryption forced to fail\n");
+      write_status (STATUS_DECRYPTION_FAILED);
+    }
   else if (!result || (gpg_err_code (result) == GPG_ERR_BAD_SIGNATURE
                        && opt.ignore_mdc_error))
     {