upgrade-rhodes-app - uninitialized constant YAML (NameError)

When I run upgrade-rhodes-app I get the error:

bin/upgrade-rhodes-app:8:in `<top (required)>': uninitialized constant YAML (NameError)

from bin/upgrade-rhodes-app:23:in `load'
from bin/upgrade-rhodes-app:23:in `<main>'
from bin/ruby_executable_hooks:24:in `eval'
from bin/ruby_executable_hooks:24:in `<main>'

which, since years, I always solve by adding:

require 'yaml'

to bin/upgrade-rhodes-app.

Is there another way to solve this?

Thanks!