diff --git a/.github/workflows/stable_api.yml b/.github/workflows/stable_api.yml
index 21f551b..e563b13 100644
--- a/.github/workflows/stable_api.yml
+++ b/.github/workflows/stable_api.yml
@@ -8,7 +8,6 @@ jobs:
     strategy:
       matrix:
         ruby:
-          - '3.0'
           - '3.1'
           - '3.2'
           - '3.3'
diff --git a/README.md b/README.md
index 80feeb0..8daddf4 100644
--- a/README.md
+++ b/README.md
@@ -153,7 +153,7 @@ On macOS using Homebrew, run:
 
 ### Supported Rubies
 
-* MRI (3.0, 3.2, 3.3)
+* MRI (3.1, 3.2, 3.3)
 * JRuby
 * TruffleRuby
 
diff --git a/cztop.gemspec b/cztop.gemspec
index 39246bb..7364530 100644
--- a/cztop.gemspec
+++ b/cztop.gemspec
@@ -33,6 +33,9 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "pry"
   spec.add_development_dependency "yard"
   spec.add_development_dependency "rubocop", "~> 1.36.0"
-  spec.add_development_dependency "async", ">= 2.0.1"
-  spec.add_development_dependency "async-io"
+
+  if RUBY_VERSION >= '3.1'
+    spec.add_development_dependency "async", ">= 2.0.1"
+    spec.add_development_dependency "async-io"
+  end
 end
diff --git a/spec/cztop/async_spec.rb b/spec/cztop/async_spec.rb
index fb315a5..2be2fac 100644
--- a/spec/cztop/async_spec.rb
+++ b/spec/cztop/async_spec.rb
@@ -1,9 +1,11 @@
 # frozen_string_literal: true
 
 require_relative 'spec_helper'
-require_relative '../../lib/cztop/async'
 
-describe Async::IO::CZTopSocket do
+# NOTE: Async 2 requires Ruby 3.1
+describe 'Async::IO::CZTopSocket', if: RUBY_VERSION >= '3.1' do
+  require_relative '../../lib/cztop/async'
+
   i = 0
   let(:endpoint)   { "inproc://async_endpoint_socket_spec_reqrep_#{i += 1}" }
   let(:req_socket) { CZTop::Socket::REQ.new(endpoint) }