Watch a different directory than default

I use Laravel 5.2 with Elixir 5.0. When my SASS files are in default location, gulp watch works fine for me. But I added a new theme that I need to keep elsewhere (./resources/assets/themes/custom) and when I do that, gulp watch doesn't see file changes.

All the solutions to this problem I found are for an older version of Elixir - they say to use a method elixir.config.registerWatcher() which is no longer available. I read about an alternative to this method in the release notes, but that's for custom gulp tasks.

I did actually try creating such a task and it worked twice, but then gulp started showing a lot of unexpected output - I think I made it recursive, because my custom task was calling the default task in which it was created.

Is there a way to specify which directories should be watched?