Buildpack execution failed (invalid compressed data)

In rare cases the following error message could occur when deploying Ruby applications:

Cloning into '/tmp/buildpacks/heroku-buildpack-ruby'...
-----> Compiling Ruby/Rails
!
! Command: 'set -o pipefail; curl --fail --retry 3 --retry-delay 1 --connect-timeout 3 --max-time 30https://s3-external-1.amazonaws.com/heroku-buildpack-ruby/ruby-2.1.2.tgz -s -o - | tar zxf -' failed unexpectedly:
!
! gzip: stdin: invalid compressed data--format violated
! tar: Unexpected EOF in archive
! tar: Unexpected EOF in archive
! tar: Error is not recoverable: exiting now
!

This just means that the Ruby sources could not be successfully downloaded. In this case just restart the deployment.