--- old/activemodel-3.0.0.beta/lib/active_model/errors.rb  2010-03-26 12:58:30.000000000 +0100
+++ new/activemodel-3.0.0.beta/lib/active_model/errors.rb   2010-03-26 12:58:39.000000000 +0100
@@ -213,6 +213,12 @@
           messages.each {|m| full_messages << m }
         else
           attr_name = attribute.to_s.gsub('.', '_').humanize
+          if attribute.to_s.match(/\./)
+            attr_array = attribute.to_s.split('.')
+            attribute = attr_array.pop.to_sym
+            @base = attr_array.pop.singularize.camelize.constantize.new
+          end
           attr_name = @base.class.human_attribute_name(attribute, :default => attr_name)
           options = { :default => "{{attribute}} {{message}}", :attribute => attr_name }