diff --git a/uplot.gemspec b/uplot.gemspec
index d9b914d..054dc98 100644
--- a/uplot.gemspec
+++ b/uplot.gemspec
@@ -15,7 +15,7 @@ Gem::Specification.new do |spec|
   MSG
   spec.homepage      = 'https://github.com/kojix2/uplot'
   spec.license       = 'MIT'
-  spec.required_ruby_version = Gem::Requirement.new('>= 2.3.0')
+  spec.required_ruby_version = Gem::Requirement.new('>= 2.4.0')
 
   spec.files         = Dir['*.{md,txt}', '{lib,exe}/**/*']
   spec.bindir        = 'exe'