diff --git ext/bigdecimal/bigdecimal.gemspec ext/bigdecimal/bigdecimal.gemspec
index 197bdea..a7511cf 100644
--- ext/bigdecimal/bigdecimal.gemspec
+++ ext/bigdecimal/bigdecimal.gemspec
@@ -12,6 +12,7 @@ Gem::Specification.new do |s|
   s.description = "This library provides arbitrary-precision decimal floating-point number class."
   s.authors = ["Kenta Murata", "Zachary Scott", "Shigeo Kobayashi"]
   s.require_path = %[.]
+  s.required_ruby_version = '>= 2.2.0'
   s.files = %w[
     bigdecimal.gemspec
     bigdecimal.c