diff --git a/lib/less/browser.js b/lib/less/browser.js
index e6937ba0..60119e6a 100644
--- a/lib/less/browser.js
+++ b/lib/less/browser.js
@@ -7,7 +7,8 @@ var sheets = [];
 less.env = location.hostname == '127.0.0.1' ||
            location.hostname == '0.0.0.0'   ||
            location.hostname == 'localhost' ||
-           location.protocol == 'file:'     ? 'development'
+           location.protocol == 'file:'     ||
+           location.port.length > 0         ? 'development'
                                             : 'production';
 
 less.watch   = function () { return this.watchMode = true };