diff --git a/test/reline/key_actor_emacs_test.rb b/test/reline/key_actor_emacs_test.rb
index 39ef15eafc..e371d318ef 100644
--- a/test/reline/key_actor_emacs_test.rb
+++ b/test/reline/key_actor_emacs_test.rb
@@ -1,4 +1,5 @@
 require_relative 'helper'
+require 'stringio'
 
 class Reline::KeyActor::Emacs::Test < Reline::TestCase
   def setup