 `radian-directory'."
   (let ((truename (file-truename filename)))
     (string-prefix-p radian-directory truename
-                     (when (file-name-case-insensitive-p truename)
+                     (when (if (fboundp 'file-name-case-insensitive-p)
+                               (file-name-case-insensitive-p truename)
+                             (radian-with-operating-system macOS
+                               t))
                        'ignore-case))))
 
 (defmacro radian--with-silent-load (&rest body)


;; Feature `text-mode' provides a major mode for editing plain text.
(use-feature text-mode
  :config

  (add-hook 'text-mode-hook #'auto-fill-mode)

     ,@body))

(defmacro radian--with-silent-message (regexps &rest body)
  "Silencing any messages that match REGEXPS, execute BODY.
REGEXPS is a list of strings; if `message' would display a
message string (not including the trailing newline) matching any
element of REGEXPS, nothing happens. The REGEXPS need not match
