diff --git a/lib/less/node/mixin.js b/lib/less/node/mixin.js
index 0a6be4e..ed9f87a 100644
--- a/lib/less/node/mixin.js
+++ b/lib/less/node/mixin.js
@@ -20,3 +20,8 @@ tree.mixin.Call.prototype = {
         throw new(Error)("mixin " + this.selector.toCSS() + " is undefined");
     }
 };
+
+tree.mixin.Definition = function MixinDefinition(name, params) {
+    this.name = name;
+    this.params = params;
+};