diff --git a/ruby2_keywords.gemspec b/ruby2_keywords.gemspec
index 0610b4d..1340427 100644
--- a/ruby2_keywords.gemspec
+++ b/ruby2_keywords.gemspec
@@ -19,6 +19,7 @@ Gem::Specification.new do |s|
   s.files = [
     "lib/ruby2_keywords.rb",
   ]
+  s.required_ruby_version = '>= 2.0.0'
   s.add_development_dependency 'test-unit', '>= 2.2'
   s.add_development_dependency 'rake'
 end