diff --git a/actionpack/lib/action_controller/metal/mime_responds.rb b/actionpack/lib/action_controller/metal/mime_responds.rb
index c8a37c5975..800752975c 100644
--- a/actionpack/lib/action_controller/metal/mime_responds.rb
+++ b/actionpack/lib/action_controller/metal/mime_responds.rb
@@ -271,6 +271,7 @@ module ActionController #:nodoc:
       if format
         self.content_type ||= format.to_s
         lookup_context.formats = [format.to_sym]
+        lookup_context.rendered_format = lookup_context.formats.first
         collector
       else
         head :not_acceptable