diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 25456ec1e..2b3e5cc20 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -18,7 +18,7 @@ jobs:
   bundler:
     runs-on: ubuntu-latest
     container:
-      image: ruby:3.1.2
+      image: ruby:3.3.8
     steps:
       - uses: actions/checkout@v6
 
@@ -34,7 +34,7 @@ jobs:
   debian-only:
     runs-on: ubuntu-latest
     container:
-      image: debian:bookworm
+      image: debian:trixie
     steps:
       - uses: actions/checkout@v6
 
diff --git a/.ruby-version b/.ruby-version
index ef538c281..37d02a6e3 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-3.1.2
+3.3.8
diff --git a/Gemfile b/Gemfile
index 1c5a09168..2ca5f2a21 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,10 +1,13 @@
 source 'https://rubygems.org'
 
 ## This version should match the version in Debian Stable.
-## If you update the version here, also update it in .ruby-version, .cirrus.yml
-## and README.md. Then push your branch and make sure Cirrus supports that
-## version.
-ruby '3.1.2'
+## If you update the version here, also update it in .ruby-version,
+## .github/workflows/ci.yml, contrib/devtools/Dockerfile, and README.md.
+## Then push your branch and make sure CI supports that version.
+ruby '3.3.8'
+
+gem 'base64'
+gem 'csv'
 
 ## If you add a new Gem below, run `bundle install` to install it.
 group :development do
diff --git a/Gemfile.lock b/Gemfile.lock
index ee5e30e25..697040753 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -3,9 +3,11 @@ GEM
   specs:
     addressable (2.8.7)
       public_suffix (>= 2.0.2, < 7.0)
+    base64 (0.3.0)
     bigdecimal (3.1.8)
     colorator (1.1.0)
     concurrent-ruby (1.3.3)
+    csv (3.3.5)
     em-websocket (0.5.3)
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0)
@@ -93,13 +95,15 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
+  base64
+  csv
   html-proofer (~> 3.19)
   jekyll
   jekyll-redirect-from
   kramdown-parser-gfm
 
 RUBY VERSION
-   ruby 3.1.2p20
+   ruby 3.3.8p144
 
 BUNDLED WITH
    2.5.14
diff --git a/README.md b/README.md
index 5d8d05308..9012ded33 100644
--- a/README.md
+++ b/README.md
@@ -41,7 +41,7 @@ permalink: /en/2016/01/01/short-title
 ## Building
 
 This website is based on [Jekyll](https://jekyllrb.com/).  To build
-locally, [install Ruby 3.1.2](https://gorails.com/setup) using system
+locally, [install Ruby 3.3.8](https://gorails.com/setup) using system
 packages, [rvm](https://rvm.io), [rbenv](https://github.com/rbenv/rbenv), or another method. An
 alternative is to use Docker, for which instructions are available [here](./contrib/devtools/).
 Then clone this repository and change directory into it:
diff --git a/contrib/devtools/Dockerfile b/contrib/devtools/Dockerfile
index a5b4b7af9..944711cd3 100644
--- a/contrib/devtools/Dockerfile
+++ b/contrib/devtools/Dockerfile
@@ -1,4 +1,4 @@
-FROM ruby:3.1.2
+FROM ruby:3.3.8
 
 ENV NOKOGIRI_USE_SYSTEM_LIBRARIES=true
 ENV JEKYLL_ENV=production