CSS Validation Help

[Mudvayne]

.overflow {
width:770px;
padding-bottom:20px;
overflow:auto;
overflow-x:auto;
overflow-y:hidden;
}

I just want to use overflow horizontally. Above code works like charm but since overflow-x:auto; & overflow-y:hidden; isn't a valid sintax so my site's CSS isn't validated. So I removed overflow-x:auto; & overflow-y:hidden; & then the overflow works fine on Opera & Firefox. But on IE the overflow works vertically as well as horizontally. Is there any CSS code (validated) that I can use only horizontally overflow?

CSS Validator