--- mm-decode.el	2020-06-07 13:16:45.973266246 +0200
+++ mm-decode-patched.el	2020-06-07 13:15:56.861220757 +0200
@@ -1680,8 +1680,8 @@
 		    (t (y-or-n-p
 			(format "Decrypt (S/MIME) part? "))))
 		   (mm-view-pkcs7 parts from))
-	  (goto-char (point-min))
-	  (insert "Content-type: text/plain\n\n")
+;; 	  (goto-char (point-min))
+;; 	  (insert "Content-type: text/plain\n\n")
 	  (setq parts (mm-dissect-buffer t)))))
      ((equal subtype "signed")
       (unless (and (setq protocol
@@ -1745,28 +1745,11 @@
 	(save-excursion
 	  (if func
 	      (setq parts (funcall func parts ctl))
-	    (mm-sec-error
-	     'gnus-details
-	     (format "Unknown encrypt protocol (%s)" protocol)))))))
-    ;; Check the results (which are now in `parts').
-    (let ((err (get-text-property 0 'sec-error (car mm-security-handle))))
-      (if (or (not err)
-	      (not (equal subtype "encrypted")))
-	  parts
-	;; We had an error during decryption.  Report what it is.
-	(list
-	 (mm-make-handle
-	  (with-current-buffer (generate-new-buffer " *mm*")
-	    (insert "Error!  Result from decryption:\n\n"
-		    (or (get-text-property 0 'gnus-details
-					   (car mm-security-handle))
-			"")
-		    "\n\n"
-		    (or (get-text-property 0 'gnus-details
-					   (car mm-security-handle))
-			""))
-	    (current-buffer))
-	  '("text/plain")))))))
+	    (mm-set-handle-multipart-parameter
+	     mm-security-handle 'gnus-details
+	     (format "Unknown encrypt protocol (%s)" protocol))))))
+     (t nil))
+    parts))
 
 (defun mm-multiple-handles (handles)
   (and (listp handles)