How to write border-radius in less without dividing result

How can I write this css into less:

border-radius: 10px / 20px;

normally css interpret something like :

border-bottom-left-radius: 10px 20px;
border-bottom-right-radius: 10px 20px;
border-top-left-radius: 10px 20px;
border-top-right-radius: 10px 20px;

but less compilers are stupid and is dividing 10px/20px = 0.5px