diff --git a/modules/init-highlight.el b/modules/init-highlight.el
index 14db3c6a..b3a923a1 100644
--- a/modules/init-highlight.el
+++ b/modules/init-highlight.el
@@ -146,7 +146,7 @@ Return a value between 0 and 1."
 (defun exordium-x-color-luminance (color)
   "Calculate the luminance of a COLOR string (e.g. \"#ffaa00\", \"blue\").
 Return a value between 0 and 1."
-  (let* ((values (x-color-values color))
+  (let* ((values (color-values color))
          (r      (/ (car values) 256.0))
          (g      (/ (cadr values) 256.0))
          (b      (/ (caddr values) 256.0)))