diff --git a/railties/lib/initializer.rb b/railties/lib/initializer.rb
index <HASH>..<HASH> 100644
--- a/railties/lib/initializer.rb
+++ b/railties/lib/initializer.rb
@@ -101,6 +101,7 @@ module Rails
     def self.run(initializer = nil, config = nil)
       default.config = config if config
       default.config ||= Configuration.new
+      yield default.config if block_given?
       default.run(initializer)
     end
   end
Run the block passed to #run first when initializing