diff --git a/jekyll-theme-chirpy.gemspec b/jekyll-theme-chirpy.gemspec
index 2aa4744..bf56ef2 100644
--- a/jekyll-theme-chirpy.gemspec
+++ b/jekyll-theme-chirpy.gemspec
@@ -23,6 +23,8 @@ Gem::Specification.new do |spec|
     "plugin_type"       => "theme"
   }
 
+  spec.required_ruby_version = [">= 2.4", "< 3.0"]
+
   spec.add_runtime_dependency "jekyll", "~> 4.1"
   spec.add_runtime_dependency "jekyll-paginate", "~> 1.1"
   spec.add_runtime_dependency "jekyll-redirect-from", "~> 0.16"