diff --git a/Gemfile b/Gemfile
index 75ee759f..52472434 100644
--- a/Gemfile
+++ b/Gemfile
@@ -7,5 +7,7 @@ gemspec
 gem "rubocop", require: false
 gem "codeclimate-test-reporter"
 gem "concurrent-ruby", "< 1.3.9"
+# json 3.0 dropped the quirks_mode option that ActiveSupport 7.2.3.x still passes
+gem "json", "< 3"
 
 gem "rails", "~> #{ENV.fetch('RAILS_VERSION', '8.0')}"