So heroku urged me to update my old ruby project Wisdoms.nl from version 2.0.0 to 2.2.4. Should be as easy as updating the Gemfile with the new version of ruby:

ruby "2.2.4"

… but unfortunately it wasn’t. I kept getting errors about json 1.8.0 not being able to install, and that I had to get gem install json -v '1.8.0' running before I could finish the bundle update that would properly update the Gemfile.lock file.

After searching online for a while I found a number of suggestions about upgrading the version of json to 1.8.1. While that didn’t work, upgrading the version to 1.8.3 did the trick and allowed me to run a bundle update command without failures. I had added the json 1.8.3 gem line to my Gemfile to make it work:

ruby "2.2.4"
gem 'json', '1.8.3'