diff --git a/mpw b/mpw
index 1250bba..6353633 100755
--- a/mpw
+++ b/mpw
@@ -7,6 +7,7 @@ require 'rubygems'
 require 'optparse'
 require 'pathname'
 require 'locale'
+require 'set'
 require 'i18n'
 
 APP_ROOT = File.dirname(Pathname.new(__FILE__).realpath)
diff --git a/mpw-server b/mpw-server
index 688973f..d5b8fa2 100755
--- a/mpw-server
+++ b/mpw-server
@@ -7,6 +7,7 @@ require 'rubygems'
 require 'optparse'
 require 'pathname'
 require 'locale'
+require 'set'
 require 'i18n'
 
 APP_ROOT = File.dirname(Pathname.new(__FILE__).realpath)
diff --git a/mpw-ssh b/mpw-ssh
index 5674b1e..b3c5f70 100755
--- a/mpw-ssh
+++ b/mpw-ssh
@@ -7,6 +7,7 @@ require 'rubygems'
 require 'optparse'
 require 'pathname'
 require 'locale'
+require 'set'
 require 'i18n'
 
 APP_ROOT = File.dirname(Pathname.new(__FILE__).realpath)