diff --git a/railties/CHANGELOG.md b/railties/CHANGELOG.md
index 178f556460..46bdcf49f8 100644
--- a/railties/CHANGELOG.md
+++ b/railties/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Remove deprecated support to old `config.ru` that use the application class as argument of `run`.
+
+    *Rafael Mendonça França*
+
 *   Remove deprecated `environment` argument from the rails commands.
 
     *Rafael Mendonça França*
diff --git a/railties/lib/rails/commands/server/server_command.rb b/railties/lib/rails/commands/server/server_command.rb
index 6c4cc3cb86..47c3f05bb3 100644
--- a/railties/lib/rails/commands/server/server_command.rb
+++ b/railties/lib/rails/commands/server/server_command.rb
@@ -21,19 +21,6 @@ module Rails
       set_environment
     end
 
-    def app
-      @app ||= begin
-        app = super
-        if app.is_a?(Class)
-          ActiveSupport::Deprecation.warn(<<-MSG.squish)
-            Using `Rails::Application` subclass to start the server is deprecated and will be removed in Rails 6.0.
-            Please change `run #{app}` to `run Rails.application` in config.ru.
-          MSG
-        end
-        app.respond_to?(:to_app) ? app.to_app : app
-      end
-    end
-
     def opt_parser
       Options.new
     end
diff --git a/railties/test/application/server_test.rb b/railties/test/application/server_test.rb
index ab9e910aed..f4bd09903a 100644
--- a/railties/test/application/server_test.rb
+++ b/railties/test/application/server_test.rb
@@ -18,20 +18,6 @@ module ApplicationTests
       teardown_app
     end
 
-    test "deprecate support of older `config.ru`" do
-      remove_file "config.ru"
-      app_file "config.ru", <<-RUBY
-        require_relative 'config/environment'
-        run AppTemplate::Application
-      RUBY
-
-      server = Rails::Server.new(config: "#{app_path}/config.ru")
-      server.app
-
-      log = File.read(Rails.application.config.paths["log"].first)
-      assert_match(/DEPRECATION WARNING: Using `Rails::Application` subclass to start the server is deprecated/, log)
-    end
-
     test "restart rails server with custom pid file path" do
       skip "PTY unavailable" unless available_pty?