How do you retain border radius with Border Image?

[edelman]

I've written some CSS so that the border colour is a linear gradient, using Border-Image.
but when you apply it to a box with border-radius, the edge where the linear is, loses the radius.

Let's say you have a DIV, with a white background, and a 10px border radius. you then apply a border-image to the bottom border say multiple colours. That then loses the radius on the corners.

How do you retain it?

Thanks
Simon