diff --git a/Gemfile b/Gemfile
index 09f0589..cd7fbc8 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,4 +1,4 @@
-source 'https://rubygems.org'
+source ENV['GEM_SOURCE'] || 'https://rubygems.org'
 
 group :development, :test do
   gem 'rake',                    :require => false