diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2a93641..d6a9efb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,7 @@
 # Development (unreleased)
 
+* Fix bundling and CONTRIBUTE.md instructions: https://github.com/DatabaseCleaner/database_cleaner-active_record/pull/123
+
 ## v2.2.1 2025-05-13
 
 * https://github.com/DatabaseCleaner/database_cleaner-active_record/pull/111 by @tagliala
diff --git a/CONTRIBUTE.md b/CONTRIBUTE.md
new file mode 100644
index 0000000..4c0940c
--- /dev/null
+++ b/CONTRIBUTE.md
@@ -0,0 +1,32 @@
+# Guidelines for contributing
+
+## 1. Fork & Clone
+
+Since you probably don't have rights to the main repo, you should Fork it (big
+button up top). After that, clone your fork locally and optionally add an
+upstream:
+
+    git remote add upstream git@github.com:DatabaseCleaner/database_cleaner-active_record.git
+
+## 2. Make sure the tests run fine
+
+The gem uses Appraisal to configure different Gemfiles to test different Rails versions.
+
+- You can run all the databases through docker if needed with `docker compose up` (you can also have them running on your system, just comment out the ones you don't need from the `docker-compose.yml` file)
+- Copy `spec/support/sample.config.yml` to `spec/support/config.yml` and edit it
+- `BUNDLE_GEMFILE=gemfiles/rails_6.1.gemfile bundle install` (change `6.1` with any version from the `gemfiles` directory)
+- `BUNDLE_GEMFILE=gemfiles/rails_6.1.gemfile bundle exec rake`
+
+Note that if you don't have all the supported databases installed and running,
+some tests will fail.
+
+> Note that you can check the `.github/workflows/ci.yml` file for different combinations of Ruby and Rails that are expected to work
+
+## 3. Prepare your contribution
+
+This is all up to you but a few points should be kept in mind:
+
+- Please write tests for your contribution
+- Make sure that previous tests still pass
+- Push it to a branch of your fork
+- Submit a pull request
diff --git a/database_cleaner-active_record.gemspec b/database_cleaner-active_record.gemspec
index 8c87e43..d4bd788 100644
--- a/database_cleaner-active_record.gemspec
+++ b/database_cleaner-active_record.gemspec
@@ -18,7 +18,7 @@ Gem::Specification.new do |spec|
   spec.executables   = []
   spec.require_paths = ["lib"]
 
-  spec.add_dependency "database_cleaner-core", "~>2.0.0"
+  spec.add_dependency "database_cleaner-core", "~>2.1.0"
   spec.add_dependency "activerecord", ">= 5.a"
 
   spec.add_development_dependency "bundler"
diff --git a/docker-compose.yml b/docker-compose.yml
new file mode 100644
index 0000000..41cf4c2
--- /dev/null
+++ b/docker-compose.yml
@@ -0,0 +1,19 @@
+services:
+  postgres:
+    image: postgres:16 # specify the version needed for a given app
+    environment:
+      - POSTGRES_PASSWORD=postgres # this is required
+    ports:
+      - "127.0.0.1:5432:5432" # so we can use `localhost` as the host
+  mysql:
+    image: mysql:9.3
+    environment:
+      - MYSQL_ROOT_PASSWORD=mysql
+    ports:
+      - "127.0.0.1:3306:3306"
+  redis:
+    image: redis:6.2-alpine
+    restart: always
+    ports:
+      - "127.0.0.1:6379:6379"
+    command: redis-server --save 20 1 --loglevel warning
diff --git a/gemfiles/rails_6.1.gemfile b/gemfiles/rails_6.1.gemfile
index 35b0ed6..b2cc5ce 100644
--- a/gemfiles/rails_6.1.gemfile
+++ b/gemfiles/rails_6.1.gemfile
@@ -5,6 +5,7 @@ source "https://rubygems.org"
 gem "database_cleaner-core", git: "https://github.com/DatabaseCleaner/database_cleaner"
 gem "rails", "~> 6.1.0"
 gem "sqlite3", "~> 1.5"
+gem "concurrent-ruby", "1.3.4"
 
 group :test do
   gem "simplecov", require: false
diff --git a/gemfiles/rails_7.0.gemfile b/gemfiles/rails_7.0.gemfile
index 3cbf401..76289d4 100644
--- a/gemfiles/rails_7.0.gemfile
+++ b/gemfiles/rails_7.0.gemfile
@@ -5,6 +5,7 @@ source "https://rubygems.org"
 gem "database_cleaner-core", git: "https://github.com/DatabaseCleaner/database_cleaner"
 gem "rails", "~> 7.0.0"
 gem "sqlite3", "~> 1.7"
+gem "concurrent-ruby", "1.3.4"
 
 group :test do
   gem "simplecov", require: false
diff --git a/gemfiles/rails_7.2.gemfile b/gemfiles/rails_7.2.gemfile
index f968a14..95b90db 100644
--- a/gemfiles/rails_7.2.gemfile
+++ b/gemfiles/rails_7.2.gemfile
@@ -3,7 +3,7 @@
 source "https://rubygems.org"
 
 gem "database_cleaner-core", git: "https://github.com/DatabaseCleaner/database_cleaner"
-gem "rails", "~> 7.2.0.beta2"
+gem "rails", "~> 7.2.0"
 
 group :test do
   gem "simplecov", require: false