diff --git a/lisp/mail/rmail.el b/lisp/mail/rmail.el
index 7ddb35e8c79..9bd925c45f3 100644
--- a/lisp/mail/rmail.el
+++ b/lisp/mail/rmail.el
@@ -110,7 +110,7 @@ Called with region narrowed to unformatted header.")
 ;;; that knows the exact ordering of the \\( \\) subexpressions.
 (defvar rmail-unix-mail-delimiter
   (let ((time-zone-regexp
-	 (concat "\\([A-Z]?[A-Z][A-Z]T\\( DST\\)?"
+	 (concat "\\([A-Z]?[A-Z][A-Z][A-Z]\\( DST\\)?"
 		 "\\|[-+]?[0-9][0-9][0-9][0-9]"
 		 "\\|"
 		 "\\) *")))