diff --git a/activejob/lib/active_job/railtie.rb b/activejob/lib/active_job/railtie.rb
index 2f6d351b99..3064a591e7 100644
--- a/activejob/lib/active_job/railtie.rb
+++ b/activejob/lib/active_job/railtie.rb
@@ -13,23 +13,28 @@ module ActiveJob
       ActiveSupport.on_load(:active_job) { self.logger = ::Rails.logger }
     end
 
-    initializer "active_job.set_configs" do
-      config.after_initialize do |app|
-        options = app.config.active_job
-        options.queue_adapter ||= :async
-
-        custom_serializers = options.delete(:custom_serializers)
+    initializer "active_job.custom_serializers" do |app|
+      config.after_initialize do
+        custom_serializers = app.config.active_job.delete(:custom_serializers)
         ActiveJob::Serializers.add_serializers custom_serializers
+      end
+    end
 
-        ActiveSupport.on_load(:active_job) do
-          options.each { |k, v| send("#{k}=", v) }
-        end
+    initializer "active_job.set_configs" do |app|
+      options = app.config.active_job
+      options.queue_adapter ||= :async
 
-        ActiveSupport.on_load(:action_dispatch_integration_test) do
-          include ActiveJob::TestHelper
+      ActiveSupport.on_load(:active_job) do
+        options.each do  |k, v|
+          k = "#{k}="
+          send(k, v) if respond_to? k
         end
       end
 
+      ActiveSupport.on_load(:action_dispatch_integration_test) do
+        include ActiveJob::TestHelper
+      end
+
       ActiveSupport.on_load(:active_record) do
         self.destroy_association_async_job = ActiveRecord::DestroyAssociationAsyncJob
       end
diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index 0b7d080428..eb7671b87b 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -2379,17 +2379,6 @@ module ApplicationTests
       assert_equal "async", ActionView::Helpers::AssetTagHelper.image_decoding
     end
 
-    test "raises when unknown configuration option is set for ActiveJob" do
-      add_to_config <<-RUBY
-        config.active_job.unknown = "test"
-      RUBY
-
-      assert_raise(NoMethodError) do
-        app "development"
-        ActiveJob::Base # load active_job
-      end
-    end
-
     test "ActiveJob::Base.retry_jitter is 0.15 by default for new apps" do
       app "development"