diff --git a/jekyll-haml-markup.gemspec b/jekyll-haml-markup.gemspec
index cdfe75a..d2ba168 100644
--- a/jekyll-haml-markup.gemspec
+++ b/jekyll-haml-markup.gemspec
@@ -21,6 +21,8 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 
+  spec.required_ruby_version = '>= 2.1.0'
+
   spec.add_development_dependency "bundler", "~> 1.16"
   spec.add_development_dependency "rake", "~> 10.0"
   spec.add_development_dependency "minitest", "~> 5.0"