diff --git a/lib/rhino/context.rb b/lib/rhino/context.rb
index e643791..801f2b8 100644
--- a/lib/rhino/context.rb
+++ b/lib/rhino/context.rb
@@ -1,3 +1,5 @@
+require 'stringio'
+
 module Rhino
 
 # ==Overview
@@ -195,4 +197,4 @@ module Rhino
 
   class RunawayScriptError < StandardError # :nodoc:
   end
-end
\ No newline at end of file
+end