diff --git a/lib/protocol/rack/adapter.rb b/lib/protocol/rack/adapter.rb
index 1fced83..28ef0bb 100644
--- a/lib/protocol/rack/adapter.rb
+++ b/lib/protocol/rack/adapter.rb
@@ -24,6 +24,10 @@ def self.new(app)
 			def self.make_response(env, response)
 				IMPLEMENTATION.make_response(env, response)
 			end
+			
+			def self.parse_file(...)
+				IMPLEMENTATION.parse_file(...)
+			end
 		end
 	end
 end
diff --git a/lib/protocol/rack/adapter/generic.rb b/lib/protocol/rack/adapter/generic.rb
index 49c0f1b..b2822a9 100644
--- a/lib/protocol/rack/adapter/generic.rb
+++ b/lib/protocol/rack/adapter/generic.rb
@@ -17,6 +17,11 @@ def self.wrap(app)
 					self.new(app)
 				end
 				
+				def self.parse_file(...)
+					# This is the old interface, which was changed in Rack 3.
+					::Rack::Builder.parse_file(...).first
+				end
+				
 				# Initialize the rack adaptor middleware.
 				# @parameter app [Object] The rack middleware.
 				def initialize(app)
diff --git a/lib/protocol/rack/adapter/rack3.rb b/lib/protocol/rack/adapter/rack3.rb
index a8e1d93..75c5761 100644
--- a/lib/protocol/rack/adapter/rack3.rb
+++ b/lib/protocol/rack/adapter/rack3.rb
@@ -15,6 +15,10 @@ def self.wrap(app)
 					self.new(app)
 				end
 				
+				def self.parse_file(...)
+					::Rack::Builder.parse_file(...)
+				end
+				
 				def make_environment(request)
 					request_path, query_string = request.path.split('?', 2)
 					server_name, server_port = (request.authority || '').split(':', 2)
diff --git a/test/protocol/rack/.adapter/config.ru b/test/protocol/rack/.adapter/config.ru
new file mode 100644
index 0000000..736c90e
--- /dev/null
+++ b/test/protocol/rack/.adapter/config.ru
@@ -0,0 +1,4 @@
+
+run lambda {|env|
+	[200, {}, ["Hello World!"]]
+}
diff --git a/test/protocol/rack/adapter.rb b/test/protocol/rack/adapter.rb
index 168f279..07770f6 100644
--- a/test/protocol/rack/adapter.rb
+++ b/test/protocol/rack/adapter.rb
@@ -9,6 +9,14 @@
 require 'disable_console_context'
 require 'server_context'
 
+describe Protocol::Rack::Adapter do
+	let(:rackup_path) {File.expand_path(".adapter/config.ru", __dir__)}
+	
+	it "can load rackup files" do
+		expect(subject.parse_file(rackup_path)).to be_a(Proc)
+	end
+end
+
 describe Protocol::Rack::Adapter::Generic do
 	let(:adapter) {subject.new(lambda{})}