diff --git a/Gemfile b/Gemfile
index 3deaadf..d04fe34 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,5 +1,9 @@
 source 'https://rubygems.org'
 
+# TODO(tobias-urdin): Pin puppet to 5.5 release as of now since we
+# cannot run puppet 6.x on CentOS 7 because of an too old Ruby version.
+# The libraries jobs should be moved over to Bionic if we require 6.x
+gem 'puppet', ['~> 5.5']
 # TODO(aschultz): 0.8.x doesn't seem to work recursively, needs investigation
 gem 'modulesync', ['>=0.6.0','<0.8.0']
 # TODO(aschultz): techincally modulesync needs json which was satisfied by