diff --git a/rucaptcha.gemspec b/rucaptcha.gemspec
index 0272f0f..75a3801 100644
--- a/rucaptcha.gemspec
+++ b/rucaptcha.gemspec
@@ -4,14 +4,16 @@ $LOAD_PATH.unshift lib unless $LOAD_PATH.include?(lib)
 require 'rucaptcha/version'
 
 Gem::Specification.new do |s|
-  s.name          = 'rucaptcha'
-  s.version       = RuCaptcha::VERSION
-  s.authors       = ['Jason Lee']
-  s.email         = 'huacnlee@gmail.com'
-  s.files         = Dir.glob('lib/**/*') + Dir.glob('app/**/*') + Dir.glob('config/**/*') + %w(README.md CHANGELOG.md)
-  s.homepage      = 'https://github.com/huacnlee/rucaptcha'
-  s.require_paths = ['lib']
-  s.summary       = 'This is a Captcha gem for Rails Application. It run ImageMagick command to draw Captcha image.'
+  s.name                  = 'rucaptcha'
+  s.version               = RuCaptcha::VERSION
+  s.authors               = 'Jason Lee'
+  s.email                 = 'huacnlee@gmail.com'
+  s.files                 = Dir.glob('lib/**/*') + Dir.glob('app/**/*') + Dir.glob('config/**/*') + %w(README.md CHANGELOG.md)
+  s.homepage              = 'https://github.com/huacnlee/rucaptcha'
+  s.require_paths         = ['lib']
+  s.summary               = 'This is a Captcha gem for Rails Application. It run ImageMagick command to draw Captcha image.'
+  s.license               = "MIT"
+  s.required_ruby_version = ">= 1.9.0"
 
   s.add_dependency 'railties', '>= 3.2'
 end