diff --git a/lisp/mail/rfc2047.el b/lisp/mail/rfc2047.el
index 66760a6595b..db6c0423a54 100644
--- a/lisp/mail/rfc2047.el
+++ b/lisp/mail/rfc2047.el
@@ -265,7 +265,8 @@ Should be called narrowed to the head of the message."
 		 (if (= (length charsets) 1)
 		     (cons (mm-charset-to-coding-system (car charsets))
 			   mm-coding-system-priorities)
-		   mm-coding-system-priorities)))
+		   mm-coding-system-priorities))
+                (case-fold-search t))
 	    (while (setq elem (pop alist))
 	      (when (or (and (stringp (car elem))
 			     (looking-at (car elem)))