I am having a weird problem. I am trying to validate my CSS but I get this error. (both in CSS 2.1 and CSS 3)

ERROR:
215 #overlay Parse Error - opacity=60)
216 #overlay Property -moz-opacity doesn't exist : 0.6
217 #overlay Property opacity doesn't exist : 0.6

Code:
215 filter:alpha(opacity=60);
216 -moz-opacity: 0.6;
217 opacity: 0.6;

I know the 'moz' attributes are CSS3, but is there any way around this so I can validate?