What you have

  • A currently existing django project, hosted on heroku, with a bunch of css

What you want

  • to have your css compiled from sass
  • for that compilation to be done with ruby, during the heroku build

How you get it

heroku setup

# bash

heroku buildpacks:add heroku/ruby --index 1 --app $APP_NAME

django pipeline setup

# config/settings/base.py

# snipped to only the relevant bit, see django pipeline's docs for the rest
    'COMPILERS': (

sass setup

# Gemfile

source "https://rubygems.org"
ruby '2.3.3'

gem "sass"
gem "susy"

Ok but that didn't work

or at least it didn't for me, I got this (formatted for readability) error

pipeline.exceptions.CompilerError: <filter object at 0x1337> exit code 1
b"/tmp/DIR/vendor/ruby-2.3.3/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require':
    cannot load such file -- bundler/setup (LoadError)
    from /tmp/DIR/vendor/ruby-2.3.3/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
    from /tmp/DIR/vendor/bundle/bin/sass:15:in `<main>"

From that message, it occurred to me that maybe python wasn't calling the right sass. Which inspired the following "fix"

How you get it, but for real this time

Install your gems to whatever ruby / sass the python buildpack is calling

# bin/pre_compile
gem install bundler
bundle install

(pre_compile is a hook for the python buildpack)

Does this mean heroku buildpacks:add heroku/ruby --index 1 is unused? Someone investigate this and let me know.

Get this fixed for good!

One of the devs of the projects below will know what's up

But if you want a fix for your project, the pre_compile script will work fine