diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2de5358e..84485c82 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -41,6 +41,7 @@ Features:
 - [#1340](https://github.com/rails-api/active_model_serializers/pull/1340) Add support for resource-level meta. (@beauby)
 
 Fixes:
+- [#1657](https://github.com/rails-api/active_model_serializers/pull/1657) Add missing missing require "active_support/json". (@andreaseger)
 - [#1661](https://github.com/rails-api/active_model_serializers/pull/1661) Fixes `read_attribute_for_serialization` not
   seeing methods defined in serialization superclass (#1653, #1658, #1660), introduced in #1650. (@bf4)
 - [#1651](https://github.com/rails-api/active_model_serializers/pull/1651) Fix deserialization of nil relationships. (@NullVoxPopuli)
diff --git a/lib/active_model_serializers.rb b/lib/active_model_serializers.rb
index 192b414b..15551f4b 100644
--- a/lib/active_model_serializers.rb
+++ b/lib/active_model_serializers.rb
@@ -2,6 +2,7 @@ require 'active_model'
 require 'active_support'
 require 'active_support/core_ext/object/with_options'
 require 'active_support/core_ext/string/inflections'
+require 'active_support/json'
 module ActiveModelSerializers
   extend ActiveSupport::Autoload
   autoload :Model
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 66609eaf..2e9c80f6 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -14,7 +14,6 @@ require 'rails'
 require 'action_controller'
 require 'action_controller/test_case'
 require 'action_controller/railtie'
-require 'active_support/json'
 require 'active_model_serializers'
 require 'fileutils'
 FileUtils.mkdir_p(File.expand_path('../../tmp/cache', __FILE__))