diff --git a/.github/workflows/ruby.yml b/.github/workflows/ruby.yml
index 5066ed8..fb51774 100644
--- a/.github/workflows/ruby.yml
+++ b/.github/workflows/ruby.yml
@@ -22,6 +22,7 @@ jobs:
           - 3.1.4
           - 3.2.2
           - 3.3.0
+          - 3.4.1
         mongo-image:
           - mongo:4.4
         include:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5f2ad77..76ed9b2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,4 +12,5 @@
 - PR-52 Masato Ikeda <masato.ikeda@gmail.com> Add MongoDB 6.0 and 7.0 to CI
 - PR-53 Masato Ikeda <masato.ikeda@gmail.com> Add Ruby 3.2 to CI matrix
 - PR-54 Masato Ikeda <masato.ikeda@gmail.com> Add Ruby 3.3 to CI matrix
+- PR-57 Masato Ikeda <masato.ikeda@gmail.com> Add Ruby 3.4 to CI matrix
 - PR-59 Masato Ikeda <masato.ikeda@gmail.com> Add MongoDB 8.0 to CI matrix
diff --git a/Gemfile b/Gemfile
index 8bb5323..ec8020e 100644
--- a/Gemfile
+++ b/Gemfile
@@ -3,6 +3,11 @@ gemspec
 
 gem 'rake'
 
+if RUBY_VERSION >= '3.4'
+  # the activesupport gem depends on the bigdecimal gem, which has been extracted as a bundled gem since Ruby 3.4.
+  gem 'bigdecimal'
+end
+
 group(:test) do
   gem 'rspec'
   gem 'log_buddy'
diff --git a/Gemfile.lock b/Gemfile.lock
index 90e7af7..767ccb5 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -7,6 +7,7 @@ PATH
 GEM
   remote: https://rubygems.org/
   specs:
+    bigdecimal (3.1.9)
     bson (5.0.2)
     byebug (11.1.3)
     coderay (1.1.3)
@@ -74,6 +75,7 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
+  bigdecimal
   byebug
   guard
   guard-bundler
diff --git a/README.md b/README.md
index 406d6e6..735ea90 100644
--- a/README.md
+++ b/README.md
@@ -14,6 +14,10 @@ gem install plucky
 
 See `examples/query.rb`.
 
+## Notes
+
+- if you are using Ruby >= 3.4 and Rails <= 7.0, you'll need to add the bigdecimal gem to your Gemfile
+
 ## Help
 
 https://groups.google.com/forum/#!forum/mongomapper