diff --git a/install.rb b/install.rb
index 933e5ee9a2098b6ac635ad2081e12a7193889040..d5ea1422ae2967206d7c1a96e4971431a60250fd 100644
--- a/install.rb
+++ b/install.rb
@@ -1,9 +1,6 @@
-version = ARGV.pop
+# Usage: ruby install.rb
 
-if version.nil?
-  puts "Usage: ruby install.rb version"
-  exit(64)
-end
+version = File.read(File.expand_path('../RAILS_VERSION', __FILE__)).strip
 
 %w( activesupport activemodel activerecord actionpack actionview actionmailer railties activejob ).each do |framework|
   puts "Installing #{framework}..."