diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 3dd973d64b..260bd063aa 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,9 @@
+*   Fixed serialization for records with an attribute named `format`.
+
+    Fixes #15188.
+
+    *Godfrey Chan*
+
 *   When a `group` is set, `sum`, `size`, `average`, `minimum` and `maximum`
     on a NullRelation should return a Hash.
 
diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index 4571cc0786..07eafef788 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -286,6 +286,8 @@ def init_with(coder)
 
       @new_record = false
 
+      self.class.define_attribute_methods
+
       run_callbacks :find
       run_callbacks :initialize
 
diff --git a/activerecord/test/cases/serialization_test.rb b/activerecord/test/cases/serialization_test.rb
index c46060a646..7dd1f10ce9 100644
--- a/activerecord/test/cases/serialization_test.rb
+++ b/activerecord/test/cases/serialization_test.rb
@@ -1,8 +1,11 @@
 require "cases/helper"
 require 'models/contact'
 require 'models/topic'
+require 'models/book'
 
 class SerializationTest < ActiveRecord::TestCase
+  fixtures :books
+
   FORMATS = [ :xml, :json ]
 
   def setup
@@ -65,4 +68,20 @@ def test_include_root_in_json_allows_inheritance
   ensure
     ActiveRecord::Base.include_root_in_json = original_root_in_json
   end
+
+  def test_read_attribute_for_serialization_with_format_after_init
+    klazz = Class.new(ActiveRecord::Base)
+    klazz.table_name = 'books'
+
+    book = klazz.new(format: 'paperback')
+    assert_equal 'paperback', book.read_attribute_for_serialization(:format)
+  end
+
+  def test_read_attribute_for_serialization_with_format_after_find
+    klazz = Class.new(ActiveRecord::Base)
+    klazz.table_name = 'books'
+
+    book = klazz.find(books(:awdr).id)
+    assert_equal 'paperback', book.read_attribute_for_serialization(:format)
+  end
 end
diff --git a/activerecord/test/fixtures/books.yml b/activerecord/test/fixtures/books.yml
index fb48645456..abe56752c6 100644
--- a/activerecord/test/fixtures/books.yml
+++ b/activerecord/test/fixtures/books.yml
@@ -2,8 +2,10 @@ awdr:
   author_id: 1
   id: 1
   name: "Agile Web Development with Rails"
+  format: "paperback"
 
 rfr:
   author_id: 1
   id: 2
   name: "Ruby for Rails"
+  format: "ebook"
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index 8c52ad2724..c15ee5022e 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -103,6 +103,7 @@ def except(adapter_names_to_exclude)
 
   create_table :books, force: true do |t|
     t.integer :author_id
+    t.string :format
     t.column :name, :string
     t.column :status, :integer, default: 0
     t.column :read_status, :integer, default: 0