diff --git a/spec/googleauth/client_id_spec.rb b/spec/googleauth/client_id_spec.rb
index 3a45b54..c35c802 100644
--- a/spec/googleauth/client_id_spec.rb
+++ b/spec/googleauth/client_id_spec.rb
@@ -31,6 +31,7 @@ spec_dir = File.expand_path(File.join(File.dirname(__FILE__)))
 $LOAD_PATH.unshift(spec_dir)
 $LOAD_PATH.uniq!
 
+require 'spec_helper'
 require 'fakefs/safe'
 require 'googleauth'
 
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index f989d46..c63ee4c 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -47,6 +47,10 @@ require 'rspec'
 require 'logging'
 require 'rspec/logging_helper'
 require 'webmock/rspec'
+require 'multi_json'
+
+# Preload adapter to work around Rubinius error with FakeFS
+MultiJson.use(:json_gem)
 
 # Allow Faraday to support test stubs
 Faraday::Adapter.load_middleware(:test)