diff --git a/railties/lib/rails/generators/rails/app/templates/config/boot.rb b/railties/lib/rails/generators/rails/app/templates/config/boot.rb
index ab6cb374de20fe94b208a1f092cce79a7ef6108e..f7b36a13da6ce6c38cf4fce27dd668471c83da8f 100644
--- a/railties/lib/rails/generators/rails/app/templates/config/boot.rb
+++ b/railties/lib/rails/generators/rails/app/templates/config/boot.rb
@@ -3,7 +3,7 @@
 # Set up gems listed in the Gemfile.
 gemfile = File.expand_path('../../Gemfile', __FILE__)
 begin
-  ENV['BUNDLE_GEMFILE'] = gemfile
+  ENV['BUNDLE_GEMFILE'] ||= gemfile
   require 'bundler'
   Bundler.setup
 rescue Bundler::GemNotFound => e