diff --git a/R/mime.R b/R/mime.R
index b1dc069d..d6eaf025 100644
--- a/R/mime.R
+++ b/R/mime.R
@@ -510,7 +510,7 @@ header_unstructured <- function(
   if (grepl("[^\x01-\x7F]", str)) {
 
     if (encode_unicode) {
-
+      str <- enc2utf8(str)
       str <- sprintf("=?utf-8?B?%s?=", base64enc::base64encode(charToRaw(str)), 0)
 
     } else {