diff --git a/lisp/url/url-http.el b/lisp/url/url-http.el
index 5832e92..f7ec640 100644
--- a/lisp/url/url-http.el
+++ b/lisp/url/url-http.el
@@ -278,14 +278,10 @@ url-http-create-request
           ;; We used to concat directly, but if one of the strings happens
           ;; to being multibyte (even if it only contains pure ASCII) then
           ;; every string gets converted with `string-MAKE-multibyte' which
-          ;; turns the 127-255 codes into things like latin-1 accented chars
-          ;; (it would work right if it used `string-TO-multibyte' instead).
+          ;; turns the 127-255 codes into things like latin-1 accented chars.
           ;; So to avoid the problem we force every string to be unibyte.
           (mapconcat
-           ;; FIXME: Instead of `string-AS-unibyte' we'd want
-           ;; `string-to-unibyte', so as to properly signal an error if one
-           ;; of the strings contains a multibyte char.
-           'string-as-unibyte
+           'string-to-unibyte
            (delq nil
             (list
              ;; The request