3 files changed, 49 insertions, 1 deletions
diff --git a/guides/source/action_controller_overview.md b/guides/source/action_controller_overview.md
index 1f9342ca25..0f46ba8698 100644
--- a/guides/source/action_controller_overview.md
+++ b/guides/source/action_controller_overview.md
@@ -619,6 +619,30 @@ It is also possible to pass a custom serializer that responds to `load` and
 Rails.application.config.action_dispatch.cookies_serializer = MyCustomSerializer
 ```
 
+When using the `:json` or `:hybrid` serializer, you should beware that not all
+Ruby objects can be serialized as JSON. For example, `Date` and `Time` objects
+will be serialized as strings, and `Hash`es will have their keys stringified.
+
+```ruby
+class CookiesController < ApplicationController
+  def set_cookie
+    cookies.encrypted[:expiration_date] = Date.tomorrow # => Thu, 20 Mar 2014
+    redirect_to action: 'read_cookie'
+  end
+
+  def read_cookie
+    cookies.encrypted[:expiration_date] # => "2014-03-20"
+  end
+end
+```
+
+It's advisable that you only store simple data (strings and numbers) in cookies.
+If you have to store complex objects, you would need to handle the conversion
+manually when reading the values on subsequent requests.
+
+If you use the cookie session store, this would apply to the `session` and
+`flash` hash as well.
+
 Rendering XML and JSON data
 ---------------------------
 
diff --git a/guides/source/active_record_querying.md b/guides/source/active_record_querying.md
index 4900f176a6..0a332d7dd9 100644
--- a/guides/source/active_record_querying.md
+++ b/guides/source/active_record_querying.md
@@ -961,7 +961,7 @@ SELECT clients.* FROM clients LEFT OUTER JOIN addresses ON addresses.client_id =
 
 WARNING: This method only works with `INNER JOIN`.
 
-Active Record lets you use the names of the [associations](association_basics.html) defined on the model as a shortcut for specifying `JOIN` clause for those associations when using the `joins` method.
+Active Record lets you use the names of the [associations](association_basics.html) defined on the model as a shortcut for specifying `JOIN` clauses for those associations when using the `joins` method.
 
 For example, consider the following `Category`, `Post`, `Comment`, `Guest` and `Tag` models:
 
diff --git a/guides/source/upgrading_ruby_on_rails.md b/guides/source/upgrading_ruby_on_rails.md
index 7467648d49..d58024df3d 100644
--- a/guides/source/upgrading_ruby_on_rails.md
+++ b/guides/source/upgrading_ruby_on_rails.md
@@ -111,6 +111,30 @@ in your application, you can add an initializer file with the following content:
 This would transparently migrate your existing `Marshal`-serialized cookies into the
 new `JSON`-based format.
 
+When using the `:json` or `:hybrid` serializer, you should beware that not all
+Ruby objects can be serialized as JSON. For example, `Date` and `Time` objects
+will be serialized as strings, and `Hash`es will have their keys stringified.
+
+```ruby
+class CookiesController < ApplicationController
+  def set_cookie
+    cookies.encrypted[:expiration_date] = Date.tomorrow # => Thu, 20 Mar 2014
+    redirect_to action: 'read_cookie'
+  end
+
+  def read_cookie
+    cookies.encrypted[:expiration_date] # => "2014-03-20"
+  end
+end
+```
+
+It's advisable that you only store simple data (strings and numbers) in cookies.
+If you have to store complex objects, you would need to handle the conversion
+manually when reading the values on subsequent requests.
+
+If you use the cookie session store, this would apply to the `session` and
+`flash` hash as well.
+
 ### Flash structure changes
 
 Flash message keys are