diff --git a/lib/simple_map_reduce/server/job_tracker.rb b/lib/simple_map_reduce/server/job_tracker.rb
index 9395b86..f66dc5c 100644
--- a/lib/simple_map_reduce/server/job_tracker.rb
+++ b/lib/simple_map_reduce/server/job_tracker.rb
@@ -13,6 +13,9 @@ class JobTracker < Sinatra::Base
         # TODO: be configurable
         MAX_WORKER_RESERVABLE_SIZE = 5
       end
+      configure :test do
+        disable :protection
+      end
       configure :development do
         register Sinatra::Reloader
       end
diff --git a/lib/simple_map_reduce/server/job_worker.rb b/lib/simple_map_reduce/server/job_worker.rb
index dd9e197..c2cc5e9 100644
--- a/lib/simple_map_reduce/server/job_worker.rb
+++ b/lib/simple_map_reduce/server/job_worker.rb
@@ -11,6 +11,9 @@ class JobWorker < Sinatra::Base
       configure do
         use Rack::Lock
       end
+      configure :test do
+        disable :protection
+      end
       configure :development do
         register Sinatra::Reloader
       end
diff --git a/simple_map_reduce.gemspec b/simple_map_reduce.gemspec
index 8e8a9c5..67b27bd 100644
--- a/simple_map_reduce.gemspec
+++ b/simple_map_reduce.gemspec
@@ -39,7 +39,7 @@ Gem::Specification.new do |spec|
   spec.add_runtime_dependency 'faraday', '>= 0.13', '< 2.8'
   spec.add_runtime_dependency 'msgpack', '>= 1.2', '< 1.5'
   spec.add_runtime_dependency 'rasteira', '~> 0.1.0'
-  spec.add_runtime_dependency 'sinatra', '~> 3.0'
-  spec.add_runtime_dependency 'sinatra-contrib', '~> 3.0'
+  spec.add_runtime_dependency 'sinatra', '~> 4.1'
+  spec.add_runtime_dependency 'sinatra-contrib', '~> 4.1'
   spec.add_runtime_dependency 'thor', '>= 0.20', '< 1.3'
 end
diff --git a/spec/server/worker_spec.rb b/spec/server/worker_spec.rb
index 9ff6bad..2aa6ed2 100644
--- a/spec/server/worker_spec.rb
+++ b/spec/server/worker_spec.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'spec_helper'
 
 RSpec.describe SimpleMapReduce::Server::Worker do
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 1c0b3d2..355a22f 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -3,6 +3,8 @@
 require 'bundler/setup'
 require 'simple_map_reduce'
 require 'rack/test'
+Rack::Test.send(:remove_const, :DEFAULT_HOST)
+Rack::Test::DEFAULT_HOST = 'localhost'
 require 'factory_bot'
 
 ENV['RACK_ENV'] = 'test'