Debug Javascript with multi-level source maps

I have a lot of javascript files, which goes through grunt uglify and gets minified individually, and further, I am performing grunt concat on these to get a single bundled minified file with source map.

Ex.

a.js, b.js, c.js ->
Uglify -> a.min.js, b.min.js,c.min.js -> concat -> bundle.min.js

With dev tools and source map, from bundle.min.js, I can trace back only up to a.min.js/b.min.js/c.min.js. Where as my goal is to use source map to trace back up to a.js/b.js/c.js.