diff --git a/actionpack/CHANGELOG b/actionpack/CHANGELOG
index c9221c45be..2e4c049788 100644
--- a/actionpack/CHANGELOG
+++ b/actionpack/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Added ActionController::Base.allow_concurrency to control whether the application is thread-safe, so multi-threaded servers like WEBrick knows whether to apply a mutex around the performance of each action. Action Pack and Active Record are by default thread-safe, but many applications may not be. Turned off by default.
+
 * Added TextHelper#word_wrap(text, line_length = 80) #1449 [tuxie@dekadance.se]
 
 * Added a fall-through action for form_remote_tag that'll be used in case Javascript is unavailable #1459 [Scott Barron]. Example:
diff --git a/actionpack/lib/action_controller/base.rb b/actionpack/lib/action_controller/base.rb
index b5983f0e90..243693437f 100755
--- a/actionpack/lib/action_controller/base.rb
+++ b/actionpack/lib/action_controller/base.rb
@@ -228,6 +228,12 @@ module ActionController #:nodoc:
     @@debug_routes = true
     cattr_accessor :debug_routes
 
+    # Controls whether the application is thread-safe, so multi-threaded servers like WEBrick knows whether to apply a mutex
+    # around the performance of each action. Action Pack and Active Record are by default thread-safe, but many applications
+    # may not be. Turned off by default.
+    @@allow_concurrency = false
+    cattr_accessor :allow_concurrency
+
     # Template root determines the base from which template references will be made. So a call to render("test/template")
     # will be converted to "#{template_root}/test/template.rhtml".
     class_inheritable_accessor :template_root
diff --git a/railties/CHANGELOG b/railties/CHANGELOG
index 444a918a7c..62e7fdcaae 100644
--- a/railties/CHANGELOG
+++ b/railties/CHANGELOG
@@ -1,6 +1,6 @@
 *SVN*
 
-* Removed the mutex from the WEBrick adapter under the production environment so concurrent requests can be served
+* Made the WEBrick adapter not use a mutex around action performance if ActionController::Base.allow_concurrency is true (default is false)
 
 * Fixed that mailer generator generated fixtures/plural while units expected fixtures/singular #1457 [Scott Barron]
 
diff --git a/railties/lib/webrick_server.rb b/railties/lib/webrick_server.rb
index 137c2570ca..71df5432e1 100644
--- a/railties/lib/webrick_server.rb
+++ b/railties/lib/webrick_server.rb
@@ -65,13 +65,13 @@ class DispatchServlet < WEBrick::HTTPServlet::AbstractServlet
   def service(req, res)
     begin
       unless handle_file(req, res)
-        REQUEST_MUTEX.lock unless RAILS_ENV == 'production'
+        REQUEST_MUTEX.lock unless ActionController::Base.allow_concurrency
         unless handle_dispatch(req, res)
           raise WEBrick::HTTPStatus::NotFound, "`#{req.path}' not found."
         end
       end
     ensure
-      unless RAILS_ENV == 'production'
+      unless ActionController::Base.allow_concurrency
         REQUEST_MUTEX.unlock if REQUEST_MUTEX.locked?
       end
     end