diff --git a/lib/less/tree/color.js b/lib/less/tree/color.js
index 18fd2167..d4c6f3eb 100644
--- a/lib/less/tree/color.js
+++ b/lib/less/tree/color.js
@@ -61,7 +61,7 @@ tree.Color.prototype = {
         for (var c = 0; c < 3; c++) {
             result[c] = tree.operate(op, this.rgb[c], other.rgb[c]);
         }
-        return new(tree.Color)(result);
+        return new(tree.Color)(result, this.alpha + other.alpha);
     },
 
     toHSL: function () {