diff --git a/lisp/mail/rmailsum.el b/lisp/mail/rmailsum.el
index cc55451902a..2eda3222a47 100644
--- a/lisp/mail/rmailsum.el
+++ b/lisp/mail/rmailsum.el
@@ -786,6 +786,11 @@ the message being processed."
 		 ;; To: =?UTF-8?Q?=C5=A0t=C4=9Bp=C3=A1n_?= =?UTF-8?Q?N=C4=9Bmec?=
 		 ;; <stepnem@gmail.com>
 		 (setq from (rfc2047-decode-string from))
+                 ;; We cannot tolerate any leftover newlines in From,
+                 ;; as that disrupts the rmail-summary display.
+                 ;; Newlines can be left in From if it was malformed,
+                 ;; e.g. had unbalanced quotes.
+                 (setq from (replace-regexp-in-string "\n+" " " from))
 		 (setq len (length from))
 		 (setq mch (string-match "[@%]" from))
 		 (format "%25s"