1 files changed, 3 insertions, 1 deletions
diff --git a/actionpack/lib/action_dispatch/middleware/exception_wrapper.rb b/actionpack/lib/action_dispatch/middleware/exception_wrapper.rb
index c0532c80c4..a8f49bd3bd 100644
--- a/actionpack/lib/action_dispatch/middleware/exception_wrapper.rb
+++ b/actionpack/lib/action_dispatch/middleware/exception_wrapper.rb
@@ -1,5 +1,6 @@
 require 'action_controller/metal/exceptions'
 require 'active_support/core_ext/exception'
+require 'active_support/core_ext/class/attribute_accessors'
 
 module ActionDispatch
   class ExceptionWrapper
@@ -10,6 +11,7 @@ module ActionDispatch
       'AbstractController::ActionNotFound'         => :not_found,
       'ActionController::MethodNotAllowed'         => :method_not_allowed,
       'ActionController::NotImplemented'           => :not_implemented,
+      'ActionController::UnknownFormat'            => :not_acceptable,
       'ActionController::InvalidAuthenticityToken' => :unprocessable_entity
     )
 
@@ -75,4 +77,4 @@ module ActionDispatch
       @backtrace_cleaner ||= @env['action_dispatch.backtrace_cleaner']
     end
   end
-end
-\ No newline at end of file
+end