diff --git a/test/unit/cors_test.rb b/test/unit/cors_test.rb
index 9123f0d..2f366c2 100644
--- a/test/unit/cors_test.rb
+++ b/test/unit/cors_test.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require 'rack/builder'
 require 'minitest/autorun'
 require 'rack/test'
 require 'mocha/setup'