Less output forced to "public" folder in latest version?

Just upgraded from Laravel 5.3 to 5.4. In Laravel 5.3 I used mix like this:

.less('resources/assets/less/app.less', 'resources/assets/css/app.css')

After which I concatenated multiple css files in the 'resources/assets/css' folder into a final app.css that went to the public folder.

Now, with Laravel 5.4, the same command will output to 'public/resources/assets/css/app.css' no matter what I do.

This is clearly not what I want. Documentation is not overly clear, but doesn't suggest this should be the behavior, am I missing something?