This is a combination of [a comment from @sankage] and [a gist by
@colinpetruno]. Many thanks to them for sharing their discoveries.

[a comment from @sankage]: https://github.com/thoughtbot/paperclip/pull/2568#issuecomment-381629629
[a gist by @colinpetruno]: https://gist.github.com/colinpetruno/037de4fafa4cff695b1d7905cd6fd7c2