diff --git a/guides/source/active_record_basics.md b/guides/source/active_record_basics.md
index bd074d0055005b4e51e5931477e149bcd2231034..ef86531eef3a4efb7ad6c7a7b5536bcce64a79b5 100644
--- a/guides/source/active_record_basics.md
+++ b/guides/source/active_record_basics.md
@@ -358,7 +358,7 @@ class CreatePublications < ActiveRecord::Migration
       t.string :publisher_type
       t.boolean :single_issue
 
-      t.timestamps
+      t.timestamps null: false
     end
     add_index :publications, :publication_type_id
   end
diff --git a/guides/source/active_record_migrations.md b/guides/source/active_record_migrations.md
index 1a41fc8b4ca7f1b6f1e359aa99de05f383828d84..e76a57e164ec059abb2ff5f80cbc7573389bc441 100644
--- a/guides/source/active_record_migrations.md
+++ b/guides/source/active_record_migrations.md
@@ -39,7 +39,7 @@ class CreateProducts < ActiveRecord::Migration
       t.string :name
       t.text :description
 
-      t.timestamps
+      t.timestamps null: false
     end
   end
 end
@@ -285,7 +285,7 @@ class CreateProducts < ActiveRecord::Migration
       t.string :name
       t.text :description
 
-      t.timestamps
+      t.timestamps null: false
     end
   end
 end
@@ -826,7 +826,7 @@ class CreateProducts < ActiveRecord::Migration
       create_table :products do |t|
         t.string :name
         t.text :description
-        t.timestamps
+        t.timestamps null: false
       end
     end
 
diff --git a/guides/source/association_basics.md b/guides/source/association_basics.md
index a12f5638e3a57ff17ba45134b6098e3672faaffc..3a2e522fa778844f1fb582ed0483b6932a2bdd38 100644
--- a/guides/source/association_basics.md
+++ b/guides/source/association_basics.md
@@ -101,13 +101,13 @@ class CreateOrders < ActiveRecord::Migration
   def change
     create_table :customers do |t|
       t.string :name
-      t.timestamps
+      t.timestamps null: false
     end
 
     create_table :orders do |t|
       t.belongs_to :customer, index: true
       t.datetime :order_date
-      t.timestamps
+      t.timestamps null: false
     end
   end
 end
@@ -132,13 +132,13 @@ class CreateSuppliers < ActiveRecord::Migration
   def change
     create_table :suppliers do |t|
       t.string :name
-      t.timestamps
+      t.timestamps null: false
     end
 
     create_table :accounts do |t|
       t.belongs_to :supplier, index: true
       t.string :account_number
-      t.timestamps
+      t.timestamps null: false
     end
   end
 end
@@ -165,13 +165,13 @@ class CreateCustomers < ActiveRecord::Migration
   def change
     create_table :customers do |t|
       t.string :name
-      t.timestamps
+      t.timestamps null: false
     end
 
     create_table :orders do |t|
       t.belongs_to :customer, index:true
       t.datetime :order_date
-      t.timestamps
+      t.timestamps null: false
     end
   end
 end
@@ -207,19 +207,19 @@ class CreateAppointments < ActiveRecord::Migration
   def change
     create_table :physicians do |t|
       t.string :name
-      t.timestamps
+      t.timestamps null: false
     end
 
     create_table :patients do |t|
       t.string :name
-      t.timestamps
+      t.timestamps null: false
     end
 
     create_table :appointments do |t|
       t.belongs_to :physician, index: true
       t.belongs_to :patient, index: true
       t.datetime :appointment_date
-      t.timestamps
+      t.timestamps null: false
     end
   end
 end
@@ -291,19 +291,19 @@ class CreateAccountHistories < ActiveRecord::Migration
   def change
     create_table :suppliers do |t|
       t.string :name
-      t.timestamps
+      t.timestamps null: false
     end
 
     create_table :accounts do |t|
       t.belongs_to :supplier, index: true
       t.string :account_number
-      t.timestamps
+      t.timestamps null: false
     end
 
     create_table :account_histories do |t|
       t.belongs_to :account, index: true
       t.integer :credit_rating
-      t.timestamps
+      t.timestamps null: false
     end
   end
 end
@@ -332,12 +332,12 @@ class CreateAssembliesAndParts < ActiveRecord::Migration
   def change
     create_table :assemblies do |t|
       t.string :name
-      t.timestamps
+      t.timestamps null: false
     end
 
     create_table :parts do |t|
       t.string :part_number
-      t.timestamps
+      t.timestamps null: false
     end
 
     create_table :assemblies_parts, id: false do |t|
@@ -371,13 +371,13 @@ class CreateSuppliers < ActiveRecord::Migration
   def change
     create_table :suppliers do |t|
       t.string  :name
-      t.timestamps
+      t.timestamps null: false
     end
 
     create_table :accounts do |t|
       t.integer :supplier_id
       t.string  :account_number
-      t.timestamps
+      t.timestamps null: false
     end
 
     add_index :accounts, :supplier_id
@@ -455,7 +455,7 @@ class CreatePictures < ActiveRecord::Migration
       t.string  :name
       t.integer :imageable_id
       t.string  :imageable_type
-      t.timestamps
+      t.timestamps null: false
     end
 
     add_index :pictures, :imageable_id
@@ -471,7 +471,7 @@ class CreatePictures < ActiveRecord::Migration
     create_table :pictures do |t|
       t.string :name
       t.references :imageable, polymorphic: true, index: true
-      t.timestamps
+      t.timestamps null: false
     end
   end
 end
@@ -501,7 +501,7 @@ class CreateEmployees < ActiveRecord::Migration
   def change
     create_table :employees do |t|
       t.references :manager, index: true
-      t.timestamps
+      t.timestamps null: false
     end
   end
 end
diff --git a/guides/source/getting_started.md b/guides/source/getting_started.md
index c2a0fde54ed79e7810eff441195b89e54db0a05a..a5e35f75a0399e73a17490ac351b88179e2747c7 100644
--- a/guides/source/getting_started.md
+++ b/guides/source/getting_started.md
@@ -677,7 +677,7 @@ class CreateArticles < ActiveRecord::Migration
       t.string :title
       t.text :text
 
-      t.timestamps
+      t.timestamps null: false
     end
   end
 end
@@ -1539,7 +1539,7 @@ class CreateComments < ActiveRecord::Migration
       # this line adds an integer column called `article_id`.
       t.references :article, index: true
 
-      t.timestamps
+      t.timestamps null: false
     end
   end
 end