I have the following line in my gemfile: gem 'client_side_validations', :git => "[email protected]:Dakuan/client_side_validations.git", :branch => "master", ref: '2245b4174ffd4b400d999cb5a2b6dccc0289eb67' The repo it's pointing at is public and I can run bundle install / update locally just fine. When I try to push to Heroku I get the following error: Fetching [email protected]:Dakuan/client_side_validations.git Host key verification failed. fatal: The remote end hung up unexpectedly Git error: command `git clone '[email protected]:Dakuan/client_side_validations.git' "/tmp/build_1xa9f06n4k1cu/vendor/bundle/ruby/1.9.1/cache/bundler/git/client_side_validations-56a04875baabb67b5f8c192c6c6743df476fd90f" --bare --no-hardlinks` in directory /tmp/build_1xa9f06n4k1cu has failed. ! ! Failed to install gems via Bundler. ! ! Heroku push rejected, failed to compile Ruby/rails app Anyone got any ideas about what's going on here?