diff --git a/lib/less/functions.js b/lib/less/functions.js
index 23d5ee5e5..95d24d7ba 100644
--- a/lib/less/functions.js
+++ b/lib/less/functions.js
@@ -206,7 +206,7 @@ tree.functions = {
         } else {
             threshold = number(threshold);
         }
-        if ((color.luma() * color.alpha) < threshold) {
+        if (color.luma() < threshold) {
             return light;
         } else {
             return dark;