diff --git a/exwm-xsettings.el b/exwm-xsettings.el
index 985c273..44b3766 100644
--- a/exwm-xsettings.el
+++ b/exwm-xsettings.el
@@ -129,20 +129,6 @@ These settings take precedence over `exwm-xsettings-theme' and
   :initialize #'custom-initialize-default
   :set #'exwm-xsettings--custom-set)
 
-(defalias 'exwm-xsettings--color-dark-p
-  (if (eval-when-compile (< emacs-major-version 29))
-      ;; Borrowed from Emacs 29.
-      (lambda (rgb)
-        "Whether RGB is more readable against white than black."
-        (unless (<= 0 (apply #'min rgb) (apply #'max rgb) 1)
-          (error "RGB components %S not in [0,1]" rgb))
-        (let* ((r (expt (nth 0 rgb) 2.2))
-               (g (expt (nth 1 rgb) 2.2))
-               (b (expt (nth 2 rgb) 2.2))
-               (y (+ (* r 0.2126) (* g 0.7152) (* b 0.0722))))
-          (< y 0.325)))
-    'color-dark-p))
-
 (defun exwm-xsettings--pick-theme (theme)
   "Pick a light or dark theme from the given THEME.
 If THEME is a string, it's returned directly.
@@ -151,7 +137,7 @@ the default face's background color."
   (pcase theme
     ((cl-type string) theme)
     (`(,(cl-type string) . ,(cl-type string))
-     (if (exwm-xsettings--color-dark-p (color-name-to-rgb (face-background 'default)))
+     (if (color-dark-p (color-name-to-rgb (face-background 'default)))
          (cdr theme) (car theme)))
     (_ (error "Expected theme to be a string or a pair of strings"))))