ASP.NET css minification fails when filter: progid:DXImageTransform.Microsoft.AlphaImageLoader is used

Question

I am minifying a bunch of css files and one of them contains

filter: progid:DXImageTransform.Microsoft.AlphaImageLoader

as a png-transparency fix for IE6 which causes the minification proccess to fail. Is there any workaround for this problem?

Thanks!