diff --git a/actionpack/lib/action_dispatch/middleware/request_id.rb b/actionpack/lib/action_dispatch/middleware/request_id.rb
index 85f95ad111..d7a1a0710c 100644
--- a/actionpack/lib/action_dispatch/middleware/request_id.rb
+++ b/actionpack/lib/action_dispatch/middleware/request_id.rb
@@ -15,9 +15,9 @@ module ActionDispatch
   # The unique request id can be used to trace a request end-to-end and would typically end up being part of log files
   # from multiple pieces of the stack.
   class RequestId
-    def initialize(app, header: nil)
+    def initialize(app, header:)
       @app = app
-      @header = header || "X-Request-Id"
+      @header = header
     end
 
     def call(env)
diff --git a/actionpack/lib/action_dispatch/railtie.rb b/actionpack/lib/action_dispatch/railtie.rb
index 99a4116a82..fa87ca7344 100644
--- a/actionpack/lib/action_dispatch/railtie.rb
+++ b/actionpack/lib/action_dispatch/railtie.rb
@@ -23,6 +23,7 @@ module ActionDispatch
     config.action_dispatch.use_authenticated_cookie_encryption = false
     config.action_dispatch.use_cookies_with_metadata = false
     config.action_dispatch.perform_deep_munge = true
+    config.action_dispatch.request_id_header = "X-Request-Id"
 
     config.action_dispatch.default_headers = {
       "X-Frame-Options" => "SAMEORIGIN",
diff --git a/actionpack/test/dispatch/request_id_test.rb b/actionpack/test/dispatch/request_id_test.rb
index da701a4a9f..b4578540e9 100644
--- a/actionpack/test/dispatch/request_id_test.rb
+++ b/actionpack/test/dispatch/request_id_test.rb
@@ -33,7 +33,7 @@ class RequestIdTest < ActiveSupport::TestCase
   end
 
   private
-    def stub_request(env = {}, header: nil)
+    def stub_request(env = {}, header: "X-Request-Id")
       ActionDispatch::RequestId.new(lambda { |environment| [ 200, environment, [] ] }, header: header).call(env)
       ActionDispatch::Request.new(env)
     end
@@ -68,7 +68,7 @@ class RequestIdResponseTest < ActionDispatch::IntegrationTest
   end
 
   private
-    def with_test_route_set(header: nil)
+    def with_test_route_set(header: "X-Request-Id")
       with_routing do |set|
         set.draw do
           get "/", to: ::RequestIdResponseTest::TestController.action(:index)