diff --git a/frameworks/Ruby/rack-app/Gemfile b/frameworks/Ruby/rack-app/Gemfile
index 2ad03adfb21..60caa764f40 100644
--- a/frameworks/Ruby/rack-app/Gemfile
+++ b/frameworks/Ruby/rack-app/Gemfile
@@ -4,6 +4,7 @@ source 'https://rubygems.org'
 
 gem 'rack-app'
 gem 'rack-app-front_end'
+gem 'cgi' # for Ruby 4.0
 gem 'iodine', '~> 0.7', platforms: %i[ruby windows]
 gem 'irb' # for Ruby 3.5
 gem 'logger' # for Ruby 3.5
diff --git a/frameworks/Ruby/rack-app/Gemfile.lock b/frameworks/Ruby/rack-app/Gemfile.lock
index 2620ee87445..c80ffdb610a 100644
--- a/frameworks/Ruby/rack-app/Gemfile.lock
+++ b/frameworks/Ruby/rack-app/Gemfile.lock
@@ -2,6 +2,7 @@ GEM
   remote: https://rubygems.org/
   specs:
     bigdecimal (3.3.1)
+    cgi (0.5.1)
     date (3.5.0)
     erb (5.1.3)
     io-console (0.8.1)
@@ -49,6 +50,7 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
+  cgi
   iodine (~> 0.7)
   irb
   json (~> 2.10)
diff --git a/frameworks/Ruby/rack-app/rack-app.dockerfile b/frameworks/Ruby/rack-app/rack-app.dockerfile
index 2b24fcab8bd..759d1eb8629 100644
--- a/frameworks/Ruby/rack-app/rack-app.dockerfile
+++ b/frameworks/Ruby/rack-app/rack-app.dockerfile
@@ -1,4 +1,4 @@
-FROM ruby:3.5-rc
+FROM ruby:4.0-rc
 
 ENV RUBY_YJIT_ENABLE=1