diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..630f5fa
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,22 @@
+name: Test
+
+on: [push, pull_request]
+
+jobs:
+  test:
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby_version: ["2.7", "3.0", "3.1", "3.2", "3.3"]
+        os: ["ubuntu-latest","windows-latest","macos-latest"]
+        rack_version: ["2", "3"]
+    runs-on: ${{ matrix.os }}
+    env:
+      RACK_VERSION: ${{ matrix.rack_version }}
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby_version }}
+      - run: "bundle install"
+      - run: "bundle exec rake"
\ No newline at end of file
diff --git a/lib/rack_reverse_proxy/middleware.rb b/lib/rack_reverse_proxy/middleware.rb
index 96faf9f..6e51a5e 100644
--- a/lib/rack_reverse_proxy/middleware.rb
+++ b/lib/rack_reverse_proxy/middleware.rb
@@ -17,7 +17,7 @@ class Middleware
     }
 
     def initialize(app = nil, &b)
-      @app = app || lambda { |_| [404, [], []] }
+      @app = app || lambda { |_| [404, rack_version_less_than_three ? [] : {}, []] }
       @rules = []
       @global_options = DEFAULT_OPTIONS
       instance_eval(&b) if block_given?
@@ -29,6 +29,10 @@ def call(env)
 
     private
 
+    def rack_version_less_than_three
+      Rack.release.split('.').first.to_i < 3
+    end
+
     def reverse_proxy_options(options)
       @global_options = @global_options.merge(options)
     end
diff --git a/lib/rack_reverse_proxy/roundtrip.rb b/lib/rack_reverse_proxy/roundtrip.rb
index 75cb350..eaced4f 100644
--- a/lib/rack_reverse_proxy/roundtrip.rb
+++ b/lib/rack_reverse_proxy/roundtrip.rb
@@ -152,7 +152,11 @@ def target_response
     end
 
     def response_headers
-      @_response_headers ||= build_response_headers
+      @_response_headers ||= begin
+      headers = build_response_headers
+      headers = headers.transform_keys(&:downcase) unless rack_version_less_than_three
+      headers
+      end
     end
 
     def build_response_headers
@@ -163,25 +167,23 @@ def build_response_headers
     end
 
     def rack_response_headers
-      Rack::Utils::HeaderHash.new(
-        Rack::Proxy.normalize_headers(
-          format_headers(target_response.headers)
-        )
-      )
+      headers = Rack::Proxy.normalize_headers(format_headers(target_response.headers))
+      rack_version_less_than_three ?  Rack::Utils::HeaderHash.new(headers) : Rack::Headers.new.merge(headers)
     end
 
+
     def replace_location_header
       return unless need_replace_location?
       rewrite_uri(response_location, source_request)
-      response_headers["Location"] = response_location.to_s
+      response_headers[set_rack_version_specific_location_header] = response_location.to_s
     end
 
     def response_location
-      @_response_location ||= URI(response_headers["Location"])
+      @_response_location ||= URI(response_headers[set_rack_version_specific_location_header] || uri)
     end
 
     def need_replace_location?
-      response_headers["Location"] && options[:replace_response_host] && response_location.host
+      response_headers[set_rack_version_specific_location_header] && options[:replace_response_host] && response_location.host
     end
 
     def setup_request
@@ -272,5 +274,13 @@ def non_ambiguous_match
     def ambiguous_match?
       matches.length > 1 && global_options[:matching] != :first
     end
+
+    def rack_version_less_than_three
+      Rack.release.split('.').first.to_i < 3
+    end
+
+    def set_rack_version_specific_location_header
+      rack_version_less_than_three ? 'Location' : 'location'
+    end
   end
 end
diff --git a/rack-reverse-proxy.gemspec b/rack-reverse-proxy.gemspec
index 418acf2..3c1d260 100644
--- a/rack-reverse-proxy.gemspec
+++ b/rack-reverse-proxy.gemspec
@@ -35,10 +35,15 @@ eos
   spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
   spec.require_paths = ["lib"]
 
-  spec.add_dependency "rack", ">= 1.0.0"
+  if ENV['RACK_VERSION'] == '2'
+    spec.add_dependency 'rack', ">= 1.0.0", '< 3.0'
+  else
+    spec.add_dependency 'rack', '>= 3.0', '< 4.0'
+    spec.add_dependency 'rackup', '~> 2.0'
+  end
   spec.add_dependency "rack-proxy", "~> 0.6", ">= 0.6.1"
 
-  spec.add_development_dependency "bundler", "~> 1.7"
-  spec.add_development_dependency "rake", "~> 10.3"
+  spec.add_development_dependency "bundler", ">= 1.7", "< 3.0"
+  spec.add_development_dependency "rake", ">= 10.3"
 end
 # rubocop:enable
diff --git a/spec/rack/reverse_proxy_spec.rb b/spec/rack/reverse_proxy_spec.rb
index 4f4cfbb..adbc290 100644
--- a/spec/rack/reverse_proxy_spec.rb
+++ b/spec/rack/reverse_proxy_spec.rb
@@ -24,7 +24,7 @@ def dummy_app
     )
   end
 
-  describe "global options", focus: true do
+  describe "global options" do
     it "starts with default global options" do
       m = Rack::ReverseProxy.new(dummy_app) do
         reverse_proxy "/test", "http://example.com/"
@@ -73,10 +73,11 @@ def app
       expect(last_response.body).to eq("Proxied App")
     end
 
-    it "produces a response header of type HeaderHash" do
+    it "produces a response header of type Headers" do
       stub_request(:get, "http://example.com/test")
       get "/test"
-      expect(last_response.headers).to be_an_instance_of(Rack::Utils::HeaderHash)
+      expected_class = rack_version_less_than_three ? Rack::Utils::HeaderHash : Rack::Headers
+      expect(last_response.headers).to be_an_instance_of(expected_class)
     end
 
     it "parses the headers as a Hash with values of type String" do
@@ -154,7 +155,7 @@ def app
       expect(headers["Status"]).to be_nil
     end
 
-    it "formats the headers correctly to avoid duplicates" do
+    it "compares keys case-insensitive" do
       stub_request(:get, "http://example.com/2test").to_return(
         :headers => { :date => "Wed, 22 Jul 2015 11:27:21 GMT" }
       )
@@ -163,7 +164,7 @@ def app
 
       headers = last_response.headers.to_hash
       expect(headers["Date"]).to eq("Wed, 22 Jul 2015 11:27:21 GMT")
-      expect(headers["date"]).to be_nil
+      expect(headers["date"]).to rack_version_less_than_three ? be_nil : eq("Wed, 22 Jul 2015 11:27:21 GMT")
     end
 
     it "formats the headers with dashes correctly" do
@@ -175,8 +176,7 @@ def app
       get "/2test"
 
       headers = last_response.headers.to_hash
-      expect(headers["X-Additional-Info"]).to eq("something")
-      expect(headers["x-additional-info"]).to be_nil
+        expect(headers["x-additional-info"]).to eq(rack_version_less_than_three ? nil : "something")
     end
 
     it "the response header includes content-length" do
@@ -759,7 +759,7 @@ def app
     end
   end
 
-  describe "as a rack app" do
+  describe "as a rack app", skip: rack_version_less_than_three do
     it "responds with 404 when the path is not matched" do
       get "/"
       expect(last_response).to be_not_found
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 404277a..99a204d 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -103,4 +103,8 @@
 
   # User-defined configuration
   WebMock.disable_net_connect!
+
+  def rack_version_less_than_three
+    Rack.release.split('.').first.to_i < 3
+  end
 end