diff --git a/Gemfile b/Gemfile
index 2ce393752..6114ca65d 100644
--- a/Gemfile
+++ b/Gemfile
@@ -13,7 +13,7 @@ gem 'hanami-router',      '~> 0.7', require: false, github: 'hanami/router',
 gem 'hanami-controller',  '~> 0.7', require: false, github: 'hanami/controller',  branch: '0.7.x'
 gem 'hanami-view',        '~> 0.7', require: false, github: 'hanami/view',        branch: '0.7.x'
 gem 'hanami-model',       '~> 0.7', require: false, github: 'hanami/model',       branch: '0.7.x'
-gem 'hanami-helpers',     '~> 0.5', require: false, github: 'hanami/helpers',     branch: 'new-routes-factory'
+gem 'hanami-helpers',     '~> 0.5', require: false, github: 'hanami/helpers',     branch: 'master'
 gem 'hanami-mailer',      '~> 0.3', require: false, github: 'hanami/mailer',      branch: '0.3.x'
 gem 'hanami-assets',      '~> 0.4', require: false, github: 'hanami/assets',      branch: 'configuration'
 
diff --git a/lib/hanami/middleware.rb b/lib/hanami/middleware.rb
index af6d38917..bf8e5d808 100644
--- a/lib/hanami/middleware.rb
+++ b/lib/hanami/middleware.rb
@@ -67,6 +67,7 @@ def call(env)
     # @see Hanami::Middleware#prepend
     def use(middleware, *args, &blk)
       stack.push [middleware, args, blk]
+      stack.uniq!
     end
 
     # Prepend a middleware to the stack.
@@ -82,6 +83,7 @@ def use(middleware, *args, &blk)
     # @see Hanami::Middleware#use
     def prepend(middleware, *args, &blk)
       stack.unshift [middleware, args, blk]
+      stack.uniq!
     end
 
     private
diff --git a/spec/isolation/middleware/ensure_unique_stack_spec.rb b/spec/isolation/middleware/ensure_unique_stack_spec.rb
new file mode 100644
index 000000000..0608cceee
--- /dev/null
+++ b/spec/isolation/middleware/ensure_unique_stack_spec.rb
@@ -0,0 +1,56 @@
+RSpec.describe Hanami::Middleware, type: :cli do
+  describe "#load!" do
+    it "loads the middleware stack without duplicates" do
+      with_project do
+        generate "action web home#index"
+        replace "apps/web/application.rb", "Application < Hanami::Application", <<-END
+class RackApp
+  def initialize(app, options = {}, &blk)
+    @app     = app
+    @options = options
+    @blk     = blk
+  end
+
+  def call(env)
+    @app.call(env)
+  end
+end
+
+class Application < Hanami::Application
+END
+
+        replace "apps/web/application.rb", "configure do", <<-END
+configure do
+  block1 = ->() {}
+  block2 = ->() {}
+  block3 = ->() {}
+
+  middleware.use Web::RackApp, foo: :bar
+  middleware.use Web::RackApp, foo: :bar # this is a duplicate and it shouldn't be included
+  middleware.use Web::RackApp, baz: :bat
+  middleware.use Web::RackApp, &block1
+  middleware.use Web::RackApp, &block1   # this is a duplicate and it shouldn't be included
+  middleware.use Web::RackApp, &block2
+
+  middleware.prepend Web::RackApp, foo: :bar # this is a duplicate and it shouldn't be included
+  middleware.prepend Web::RackApp, cap: :tain
+  middleware.prepend Web::RackApp, &block1   # this is a duplicate and it shouldn't be included
+  middleware.prepend Web::RackApp, &block2   # this is a duplicate and it shouldn't be included
+  middleware.prepend Web::RackApp, &block3
+END
+
+        require Pathname.new(Dir.pwd).join("config", "environment")
+        Hanami::Components.resolve('all')
+
+        middleware = Web::Application.new.__send__(:middleware)
+
+        # We tried to mount Web::RackApp 11 times.
+        #
+        # We have 5 duplicates marked inline.
+        #
+        # That leads us to 6 (11 - 5) mounted middleware.
+        expect(middleware.__send__(:stack).count).to be(6)
+      end
+    end
+  end
+end
diff --git a/spec/support/fixtures.rb b/spec/support/fixtures.rb
index c63f64fe7..23c2eb8a0 100644
--- a/spec/support/fixtures.rb
+++ b/spec/support/fixtures.rb
@@ -1,6 +1,6 @@
 # Please use this app only for:
 #
-#   * spec/application_spec.rb
+#   * spec/unit/application_spec.rb
 #   * spec/isolation/application_configure_spec.rb
 module UnitTesting
   class Application < Hanami::Application