diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 900f56f..ae1d568 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -4,10 +4,10 @@ on: [push, pull_request]
 
 jobs:
   tests:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby: [2.4, 2.7, 3.0, truffleruby-head]
+        ruby: [2.4, 2.7, '3.0', 3.1, truffleruby-head]
 
     steps:
     - uses: actions/checkout@master
diff --git a/.rubocop.yml b/.rubocop.yml
index 25104f3..43747b4 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -42,6 +42,9 @@ Performance/TimesMap:
   Exclude:
     - 'spec/**/**.rb'
 
+Gemspec/RequiredRubyVersion:
+  Enabled: false
+
 # TODO: Fix these...
 Style/Documentation:
   Enabled: false
diff --git a/jsonapi-serializer.gemspec b/jsonapi-serializer.gemspec
index 0732452..9cc59c7 100644
--- a/jsonapi-serializer.gemspec
+++ b/jsonapi-serializer.gemspec
@@ -12,7 +12,7 @@ Gem::Specification.new do |gem|
 
   gem.summary = 'Fast JSON:API serialization library'
   gem.description = 'Fast, simple and easy to use '\
-    'JSON:API serialization library (also known as fast_jsonapi).'
+                    'JSON:API serialization library (also known as fast_jsonapi).'
   gem.homepage = 'https://github.com/jsonapi-serializer/jsonapi-serializer'
   gem.licenses = ['Apache-2.0']
   gem.files = Dir['lib/**/*']
@@ -33,4 +33,5 @@ Gem::Specification.new do |gem|
   gem.add_development_dependency('rubocop-rspec')
   gem.add_development_dependency('simplecov')
   gem.add_development_dependency('sqlite3')
+  gem.metadata['rubygems_mfa_required'] = 'true'
 end
diff --git a/lib/fast_jsonapi/object_serializer.rb b/lib/fast_jsonapi/object_serializer.rb
index 26dd5f5..04bd98d 100644
--- a/lib/fast_jsonapi/object_serializer.rb
+++ b/lib/fast_jsonapi/object_serializer.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require 'active_support'
 require 'active_support/time'
 require 'active_support/concern'
 require 'active_support/inflector'
@@ -133,9 +134,7 @@ module FastJsonapi
       def reflected_record_type
         return @reflected_record_type if defined?(@reflected_record_type)
 
-        @reflected_record_type ||= begin
-          name.split('::').last.chomp('Serializer').underscore.to_sym if name&.end_with?('Serializer')
-        end
+        @reflected_record_type ||= (name.split('::').last.chomp('Serializer').underscore.to_sym if name&.end_with?('Serializer'))
       end
 
       def set_key_transform(transform_name)
diff --git a/lib/fast_jsonapi/serialization_core.rb b/lib/fast_jsonapi/serialization_core.rb
index 4931fa7..0cbdad0 100644
--- a/lib/fast_jsonapi/serialization_core.rb
+++ b/lib/fast_jsonapi/serialization_core.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require 'active_support'
 require 'active_support/concern'
 require 'digest/sha1'
 
diff --git a/lib/jsonapi/serializer/instrumentation.rb b/lib/jsonapi/serializer/instrumentation.rb
index 4f555df..b89a3dd 100644
--- a/lib/jsonapi/serializer/instrumentation.rb
+++ b/lib/jsonapi/serializer/instrumentation.rb
@@ -1,3 +1,4 @@
+require 'active_support'
 require 'active_support/notifications'
 
 module JSONAPI
diff --git a/spec/fixtures/_user.rb b/spec/fixtures/_user.rb
index 733f582..5a4177e 100644
--- a/spec/fixtures/_user.rb
+++ b/spec/fixtures/_user.rb
@@ -1,3 +1,4 @@
+require 'active_support'
 require 'active_support/cache'
 
 class User
diff --git a/spec/fixtures/actor.rb b/spec/fixtures/actor.rb
index f85120a..f212de1 100644
--- a/spec/fixtures/actor.rb
+++ b/spec/fixtures/actor.rb
@@ -1,3 +1,4 @@
+require 'active_support'
 require 'active_support/cache'
 require 'jsonapi/serializer/instrumentation'
 
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index c9068d7..138462e 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -6,6 +6,7 @@ SimpleCov.start do
 end
 SimpleCov.minimum_coverage 90
 
+require 'active_support'
 require 'active_support/core_ext/object/json'
 require 'jsonapi/serializer'
 require 'ffaker'