2 files changed, 7 insertions, 6 deletions
diff --git a/actionpack/lib/action_controller/metal/mime_responds.rb b/actionpack/lib/action_controller/metal/mime_responds.rb
index a072fce1a1..84ade41036 100644
--- a/actionpack/lib/action_controller/metal/mime_responds.rb
+++ b/actionpack/lib/action_controller/metal/mime_responds.rb
@@ -396,10 +396,10 @@ module ActionController #:nodoc:
     # request, with this response then being accessible by calling #response.
     class Collector
       include AbstractController::Collector
-      attr_accessor :order, :format
+      attr_accessor :format
 
       def initialize(mimes)
-        @order, @responses = [], {}
+        @responses = {}
         mimes.each { |mime| send(mime) }
       end
 
@@ -414,7 +414,6 @@ module ActionController #:nodoc:
 
       def custom(mime_type, &block)
         mime_type = Mime::Type.lookup(mime_type.to_s) unless mime_type.is_a?(Mime::Type)
-        @order << mime_type
         @responses[mime_type] ||= block
       end
 
@@ -423,7 +422,7 @@ module ActionController #:nodoc:
       end
 
       def negotiate_format(request)
-        @format = request.negotiate_mime(order)
+        @format = request.negotiate_mime(@responses.keys)
       end
     end
   end
diff --git a/actionpack/lib/action_dispatch/routing/mapper.rb b/actionpack/lib/action_dispatch/routing/mapper.rb
index db9c993590..cd5220548c 100644
--- a/actionpack/lib/action_dispatch/routing/mapper.rb
+++ b/actionpack/lib/action_dispatch/routing/mapper.rb
@@ -226,11 +226,13 @@ module ActionDispatch
               action     = action.to_s     unless action.is_a?(Regexp)
 
               if controller.blank? && segment_keys.exclude?(:controller)
-                raise ArgumentError, "missing :controller"
+                message = "Missing :controller key on routes definition, please check your routes."
+                raise ArgumentError, message
               end
 
               if action.blank? && segment_keys.exclude?(:action)
-                raise ArgumentError, "missing :action"
+                message = "Missing :action key on routes definition, please check your routes."
+                raise ArgumentError, message
               end
 
               if controller.is_a?(String) && controller !~ /\A[a-z_0-9\/]*\z/