diff --git a/Gemfile b/Gemfile
index ebdc4d7..1cf440d 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'