Thomas Miedema authored Feb 25, 2016 and Ben Gamari committed Feb 25, 2016

Fixes #10398 in a different way, thereby also fixing #11579.

I inverted the logic of the Bool argument to "worker", to hopefully make
it more self-explanatory.

Reviewers: austin, hvr, bgamari

Reviewed By: bgamari

Differential Revision: https://phabricator.haskell.org/D1935