diff --git a/lib/voight_kampff.rb b/lib/voight_kampff.rb
index 317cf1d..0eb44fb 100644
--- a/lib/voight_kampff.rb
+++ b/lib/voight_kampff.rb
@@ -1,7 +1,8 @@
 require 'json'
 
 require 'voight_kampff/test'
-require 'voight_kampff/rack_request' if defined?(Rack)
+require 'voight_kampff/methods'
+require 'voight_kampff/rack_request' if defined?(Rack::Request)
 require 'voight_kampff/engine' if defined?(Rails)
 
 module VoightKampff
diff --git a/lib/voight_kampff/engine.rb b/lib/voight_kampff/engine.rb
index aeb6a4a..6f8f96f 100644
--- a/lib/voight_kampff/engine.rb
+++ b/lib/voight_kampff/engine.rb
@@ -3,5 +3,11 @@ class Engine < Rails::Engine
     rake_tasks do
       load 'tasks/voight_kampff.rake'
     end
+
+    initializer :add_voight_kampff_methods do |app|
+      ActionDispatch::Request.class_eval do
+        include VoightKampff::Methods
+      end
+    end
   end
 end
diff --git a/lib/voight_kampff/methods.rb b/lib/voight_kampff/methods.rb
new file mode 100644
index 0000000..67e4e0e
--- /dev/null
+++ b/lib/voight_kampff/methods.rb
@@ -0,0 +1,10 @@
+module VoightKampff::Methods
+  def human?
+    VoightKampff::Test.new(user_agent).human?
+  end
+
+  def bot?
+    VoightKampff::Test.new(user_agent).bot?
+  end
+  alias :replicant? :bot?
+end
diff --git a/lib/voight_kampff/rack_request.rb b/lib/voight_kampff/rack_request.rb
index 7a78ec8..a7e1e00 100644
--- a/lib/voight_kampff/rack_request.rb
+++ b/lib/voight_kampff/rack_request.rb
@@ -1,11 +1,4 @@
 # Reopen the Rack::Request class to add bot detection methods
-class Rack::Request
-  def human?
-    VoightKampff::Test.new(user_agent).human?
-  end
-
-  def bot?
-    VoightKampff::Test.new(user_agent).bot?
-  end
-  alias :replicant? :bot?
+Rack::Request.class_eval do
+  include VoightKampff::Methods
 end
diff --git a/spec/controllers/replicants_controller_spec.rb b/spec/controllers/replicants_controller_spec.rb
index a12ce81..502df1d 100644
--- a/spec/controllers/replicants_controller_spec.rb
+++ b/spec/controllers/replicants_controller_spec.rb
@@ -3,7 +3,7 @@
 describe ReplicantsController, type: :controller do
   let(:user_agent_string) { '' }
   before do
-    expect(request).to receive(:user_agent).and_return user_agent_string
+    expect_any_instance_of(ActionController::TestRequest).to receive(:user_agent).and_return user_agent_string
     get :index
   end
 
diff --git a/voight_kampff.gemspec b/voight_kampff.gemspec
index a9dbcf6..3d8246a 100644
--- a/voight_kampff.gemspec
+++ b/voight_kampff.gemspec
@@ -23,7 +23,7 @@ Gem::Specification.new do |s|
 
   s.add_dependency 'rack', ['>= 1.4', '< 3.0']
 
-  s.add_development_dependency 'rails', '~> 4.2'
+  s.add_development_dependency 'rails', '~> 5.0'
   s.add_development_dependency 'rspec-rails', '~> 3.3'
   s.add_development_dependency 'combustion', '~> 0.5'
 end