diff --git a/Gruntfile.js b/Gruntfile.js
index <HASH>..<HASH> 100644
--- a/Gruntfile.js
+++ b/Gruntfile.js
@@ -348,7 +348,6 @@ module.exports = function ( grunt ) {
 			options: {
 				keepSpecialComments: 0,
 				banner: minBanner,
-				compatibility: 'ie9',
 				report: 'gzip'
 			},
 			dist: {
Remove IE9 compatibility flag from grunt-cssmin

The default mode in clean-css supports IE<I>+ which is sufficient for
use now: <URL>