diff --git a/lib/fakefs/safe.rb b/lib/fakefs/safe.rb
index a1b804c..09a2bbb 100644
--- a/lib/fakefs/safe.rb
+++ b/lib/fakefs/safe.rb
@@ -1,5 +1,6 @@
 require 'fileutils'
 require 'pathname'
+require 'stringio'
 require 'fakefs/base'
 require 'fakefs/fake/file'
 require 'fakefs/fake/dir'