diff --git a/.circleci/config.yml b/.circleci/config.yml
index 7da3b7b9..e5ea0304 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -27,4 +27,6 @@ workflows:
             - cimg/ruby:3.2
             - cimg/ruby:3.3
             - cimg/ruby:3.4
+            - cimg/ruby:4.0
             - jruby:9.4
+            - jruby:10.0
diff --git a/prometheus-client.gemspec b/prometheus-client.gemspec
index 549674f8..29aed5cf 100644
--- a/prometheus-client.gemspec
+++ b/prometheus-client.gemspec
@@ -16,6 +16,7 @@ Gem::Specification.new do |s|
   s.require_paths     = ['lib']
 
   s.add_dependency 'base64'
+  s.add_dependency 'cgi'
 
   s.add_development_dependency 'benchmark'
   s.add_development_dependency 'benchmark-ips'