diff --git a/collects/sirmail/sendr.ss b/collects/sirmail/sendr.ss
index bb2b1c250b..3f648394e6 100644
--- a/collects/sirmail/sendr.ss
+++ b/collects/sirmail/sendr.ss
@@ -741,7 +741,7 @@
                       [body-lines (regexp-split 
 				   #rx"\n" 
 				   (substring message-str (cdar m) (string-length message-str)))])
-		  (validate-header header)
+		  (validate-header (regexp-replace #rx"[^\x0-\xFF]" header "_"))
                   (let* ([to* (sm-extract-addresses (extract-field "To" header))]
                          [to (map encode-for-header (map car to*))]
                          [cc* (sm-extract-addresses (extract-field "CC" header))]
@@ -762,6 +762,8 @@
                          [new-header (append-headers std-header prop-header)]
                          [tos (map cdr (append to* cc* bcc*))])
 
+                    (validate-header new-header)
+
                     (as-background
                      enable
                      (lambda (break-bad break-ok)