Vertical centring image with display table-cell not working

Vertical centring image with display table-cell not working

Im trying to vertically centre an image using CSS display table-cell. WHy
is my code not working? It looks like it should according to
css-tricks.css
http://css-tricks.com/centering-in-the-unknown/
http://jsfiddle.net/sNE4y/1/
.cont {
background-color: grey;
position: fixed;
height: 100%;
width: 100%;
display: table;
}
img {
display: table-cell;
vertical-align: middle;
}
<div class="cont">
<img src="http://www.quarktet.com/Icon-small.jpg" />
</div>