@marutosi [Your comment linking the issue](https://github.com/opf/openproject/pull/2066#issuecomment-110794301) to Debian's oldstable bundler release as an exhibit of a bundler version 1.5. out in the wild is just absurd: it depends on an unsupported ruby 1.8 package and whoever still tries to use OP with it will have a completely different set of problems. Nonetheless, given the vague error message, I don't see the harm in re-introducing that warning for the poor folks still stuck with an older bundler. Let @linki drop it again when bundler 2 is finally released ;)