diff --git a/lib/less/index.js b/lib/less/index.js
index 657d9bd0..f0d4e9bf 100644
--- a/lib/less/index.js
+++ b/lib/less/index.js
@@ -19,7 +19,7 @@ var less = {
 
         if (callback) {
             parser.parse(input, function (e, root) {
-                callback(e, root.toCSS(options));
+                callback(e, root && root.toCSS && root.toCSS(options));
             });
         } else {
             ee = new(require('events').EventEmitter);