diff --git a/lib/less/browser.js b/lib/less/browser.js
index b7de8be8..f5cf6a55 100644
--- a/lib/less/browser.js
+++ b/lib/less/browser.js
@@ -17,7 +17,8 @@ less.env = less.env || (location.hostname == '127.0.0.1' ||
 // doesn't start loading before the stylesheets are parsed.
 // Setting this to `true` can result in flickering.
 //
-less.async = false;
+less.async = less.async || false;
+less.fileAsync = less.fileAsync || false;
 
 // Interval between watch polls
 less.poll = less.poll || (isFileProtocol ? 1000 : 1500);
@@ -229,7 +230,7 @@ function createCSS(styles, sheet, lastModified) {
 
 function xhr(url, type, callback, errback) {
     var xhr = getXMLHttpRequest();
-    var async = isFileProtocol ? false : less.async;
+    var async = isFileProtocol ? less.fileAsync : less.async;
 
     if (typeof(xhr.overrideMimeType) === 'function') {
         xhr.overrideMimeType('text/css');