diff --git a/guides/source/upgrading_ruby_on_rails.md b/guides/source/upgrading_ruby_on_rails.md
index b4a59fe3da5b6e8281ef3addd898fa2ab3e7c4be..59e21e9be249d018bb50f3bf3a5646b61b07fae0 100644
--- a/guides/source/upgrading_ruby_on_rails.md
+++ b/guides/source/upgrading_ruby_on_rails.md
@@ -82,6 +82,8 @@ becomes
 get 'こんにちは', controller: 'welcome', action: 'index'
 ```
 
+* Rails 4.0 has removed ActionDispatch::BestStandardsSupport middleware, !DOCTYPE html already triggers standards mode per http://msdn.microsoft.com/en-us/library/jj676915(v=vs.85).aspx and ChromeFrame header has been moved to `config.action_dispatch.default_headers`
+
 ### Active Support
 
 Rails 4.0 removes the `j` alias for `ERB::Util#json_escape` since `j` is already used for `ActionView::Helpers::JavaScriptHelper#escape_javascript`.