diff --git a/tool/mkrunnable.rb b/tool/mkrunnable.rb
index 73b846026e..10f8c293c5 100755
--- a/tool/mkrunnable.rb
+++ b/tool/mkrunnable.rb
@@ -1,6 +1,7 @@
 #!./miniruby
 # -*- coding: us-ascii -*-
 
+require './rbconfig'
 require 'fileutils'
 
 case ARGV[0]