diff --git a/Gemfile b/Gemfile
index 8552f4d..982eb5a 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,10 +1,10 @@
 source 'https://rubygems.org'
 
 gem 'rake'
-gem 'mongoid', '~> 7'
+gem 'mongoid', '~> 9'
 
 group :test do
   gem 'rspec', '~> 2'
   gem 'rdoc'
-  gem 'database_cleaner'
+  gem 'database_cleaner-mongoid'
 end
diff --git a/lib/mongoid/taggable.rb b/lib/mongoid/taggable.rb
index 31c583a..a2a224a 100644
--- a/lib/mongoid/taggable.rb
+++ b/lib/mongoid/taggable.rb
@@ -22,7 +22,9 @@ module Mongoid::Taggable
 
     # add callback to save tags index
     after_save do |document|
-      document.class.save_tags_index! if document.tags_array_changed?
+      # Use previously_changed? as Mongoid 8.x+ updates attributes before after_save so changed? returns false here 
+      # see: https://www.mongodb.com/docs/mongoid/8.1/release-notes/mongoid-8.0/#changeable-module-behavior-made-compatible-with-activemodel--dirty
+      document.class.save_tags_index! if document.tags_array_previously_changed?
     end
 
     # enable indexing as default
diff --git a/mongoid_taggable.gemspec b/mongoid_taggable.gemspec
index a7335e0..6cbb026 100644
--- a/mongoid_taggable.gemspec
+++ b/mongoid_taggable.gemspec
@@ -19,5 +19,5 @@ Gem::Specification.new do |g|
   g.require_paths = ['lib']
 
   g.add_runtime_dependency 'rake', '>= 0'
-  g.add_runtime_dependency 'mongoid', '~> 7'
+  g.add_runtime_dependency 'mongoid', '~> 9'
 end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 835eeae..0e7590c 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -1,14 +1,14 @@
 $: << File.expand_path("../../lib", __FILE__)
 
-require 'database_cleaner'
+require 'database_cleaner-mongoid'
 
 RSpec.configure do |config|
   config.before(:suite) do
-    DatabaseCleaner.strategy = :truncation
+    DatabaseCleaner[:mongoid].strategy = :deletion
   end
 
   config.after(:each) do
-    DatabaseCleaner.clean
+    DatabaseCleaner[:mongoid].clean
   end
 end
 
@@ -16,4 +16,3 @@
 require 'mongoid_taggable'
 
 Mongoid.load!("spec/mongoid.yml", :test)
-