diff --git a/fluent-plugin-parser_cef.gemspec b/fluent-plugin-parser_cef.gemspec
index 9658c42..e484957 100644
--- a/fluent-plugin-parser_cef.gemspec
+++ b/fluent-plugin-parser_cef.gemspec
@@ -17,7 +17,7 @@ Gem::Specification.new do |spec|
   spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
   spec.require_paths = ["lib"]
 
-  spec.required_ruby_version = "~> 2.1"
+  spec.required_ruby_version = ">= 2.1"
 
   spec.add_runtime_dependency "fluentd", ">= 0.14.0", "< 2"