diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5dee180f8..e7eddf8d3 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -12,16 +12,16 @@ jobs:
       fail-fast: false
       matrix:
         os: [ ubuntu, macos, windows ]
-        ruby: [ 3.2.9, 3.3.9, 3.4.7 ]
+        ruby: [ 3.2.9, 3.3.10, 3.4.8, 4.0.0 ]
         mspecopt: [""]
         rubyopt: [""]
         exclude:
           - { os: windows, ruby: 3.2.9 } # 3.2.9 has some issue with file time microseconds
         include:
           - { os: windows, ruby: 3.2.8 } # 3.2.9 has some issue with file time microseconds
-          - { os: ubuntu, ruby: 3.4.7, mspecopt: "--repeat 2" }
-          - { os: ubuntu, ruby: 3.4.7, rubyopt: "--enable-frozen-string-literal" }
-          - { os: ubuntu, ruby: 3.4.7, rubyopt: "--parser=parse.y" }
+          - { os: ubuntu, ruby: 4.0.0, mspecopt: "--repeat 2" }
+          - { os: ubuntu, ruby: 4.0.0, rubyopt: "--enable-frozen-string-literal" }
+          - { os: ubuntu, ruby: 4.0.0, rubyopt: "--parser=parse.y" }
 
     runs-on: ${{ matrix.os }}-latest
     steps:
@@ -78,5 +78,5 @@ jobs:
     - uses: actions/checkout@v6
     - uses: ruby/setup-ruby@v1
       with:
-        ruby-version: '3.4'
+        ruby-version: '4.0'
     - run: bin/rubocop
diff --git a/language/magic_comment_spec.rb b/language/magic_comment_spec.rb
index f2bf3a08e..90bb83e27 100644
--- a/language/magic_comment_spec.rb
+++ b/language/magic_comment_spec.rb
@@ -45,10 +45,19 @@
 
 describe "Magic comments" do
   describe "in stdin" do
-    it_behaves_like :magic_comments, :locale, -> file {
-      print_at_exit = fixture(__FILE__, "print_magic_comment_result_at_exit.rb")
-      ruby_exe(nil, args: "< #{fixture(__FILE__, file)}", options: "-r#{print_at_exit}")
-    }
+    ruby_version_is ""..."4.0" do
+      it_behaves_like :magic_comments, :locale, -> file {
+        print_at_exit = fixture(__FILE__, "print_magic_comment_result_at_exit.rb")
+        ruby_exe(nil, args: "< #{fixture(__FILE__, file)}", options: "-r#{print_at_exit}")
+      }
+    end
+
+    ruby_version_is "4.0" do
+      it_behaves_like :magic_comments, :UTF8, -> file {
+        print_at_exit = fixture(__FILE__, "print_magic_comment_result_at_exit.rb")
+        ruby_exe(nil, args: "< #{fixture(__FILE__, file)}", options: "-r#{print_at_exit}")
+      }
+    end
   end
 
   platform_is_not :windows do
diff --git a/library/socket/shared/address.rb b/library/socket/shared/address.rb
index 3857a40ce..b548f1eac 100644
--- a/library/socket/shared/address.rb
+++ b/library/socket/shared/address.rb
@@ -173,7 +173,7 @@
       end
     end
 
-    guard -> { platform_is :windows and ruby_bug "#21702", ""..."4.0" } do
+    guard -> { platform_is :windows and ruby_bug "#21702", ""..."4.1" } do
       it 'equals address of peer socket' do
         if @method == :local_address
           @addr.to_s.should == @b.remote_address.to_s
diff --git a/library/socket/unixsocket/recvfrom_spec.rb b/library/socket/unixsocket/recvfrom_spec.rb
index 7fa5c9b60..9bb18047c 100644
--- a/library/socket/unixsocket/recvfrom_spec.rb
+++ b/library/socket/unixsocket/recvfrom_spec.rb
@@ -32,7 +32,7 @@
       end
     end
 
-    guard -> { platform_is :windows and ruby_bug "#21702", ""..."4.0" } do
+    guard -> { platform_is :windows and ruby_bug "#21702", ""..."4.1" } do
       it "returns an array containing basic information on the client as second element" do
         @client.send("foobar", 0)
         sock = @server.accept
@@ -54,7 +54,7 @@
       end
     end
 
-    guard -> { platform_is :windows and ruby_bug "#21702", ""..."4.0" } do
+    guard -> { platform_is :windows and ruby_bug "#21702", ""..."4.1" } do
       it "returns an array containing server's address as second element" do
         @client.send("", 0)
         sock = @server.accept
@@ -131,7 +131,7 @@
       end
     end
 
-    guard -> { platform_is :windows and ruby_bug "#21702", ""..."4.0" } do
+    guard -> { platform_is :windows and ruby_bug "#21702", ""..."4.1" } do
       it 'returns an Array containing the data and address information' do
         @server.recvfrom(5).should == ['hello', ['AF_UNIX', '']]
       end