diff --git a/.ruby-version b/.ruby-version
index 7921bd0c8..d13e837c8 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-3.4.8
+4.0.6
diff --git a/Dockerfile b/Dockerfile
index fe6469c5c..3df99fabc 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM ruby:3.4.8
+FROM ruby:4.0.6
 
 # Default node version on apt is old. This makes sure a recent version is installed
 # This step also runs apt-get update
diff --git a/Gemfile b/Gemfile
index ff349d581..e5ef74f4d 100644
--- a/Gemfile
+++ b/Gemfile
@@ -40,6 +40,7 @@ gem 'premailer-rails'
 
 gem 'pundit'
 gem 'reline' # LOCKED: Added because of readline is not part of Ruby 3.5.0
+gem 'readline' # LOCKED: readline was loaded from the standard library, but is not part of the default gems starting from Ruby 4.0.0.
 gem 'rolify'
 # Use Sass to process CSS
 gem 'sassc-rails'
diff --git a/Gemfile.lock b/Gemfile.lock
index baa1f771e..77a53d5a1 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -459,6 +459,8 @@ GEM
       prism (>= 1.6.0)
       rbs (>= 4.0.0)
       tsort
+    readline (0.0.4)
+      reline
     regexp_parser (2.12.0)
     reline (0.6.3)
       io-console (~> 0.5)
@@ -684,6 +686,7 @@ DEPENDENCIES
   rails (~> 8.1.2)
   rails-html-sanitizer (~> 1.7.0)
   rails_semantic_logger
+  readline
   reline
   rolify
   rollbar
@@ -888,6 +891,7 @@ CHECKSUMS
   rb-inotify (0.11.1) sha256=a0a700441239b0ff18eb65e3866236cd78613d6b9f78fea1f9ac47a85e47be6e
   rbs (4.0.3) sha256=5a7bf70e2628549d9a1f44eae447b2cfe55968a9c60cfff52693a4bdcc020e14
   rdoc (8.0.0) sha256=03bf8c08a9639658855a0cfd77c0abca8325c227693f7f33f82957811348c469
+  readline (0.0.4) sha256=6138eef17be2b98298b672c3ea63bf9cb5158d401324f26e1e84f235879c1d6a
   regexp_parser (2.12.0) sha256=35a916a1d63190ab5c9009457136ae5f3c0c7512d60291d0d1378ba18ce08ebb
   reline (0.6.3) sha256=1198b04973565b36ec0f11542ab3f5cfeeec34823f4e54cebde90968092b1835
   rexml (3.4.4) sha256=19e0a2c3425dfbf2d4fc1189747bdb2f849b6c5e74180401b15734bc97b5d142
@@ -955,7 +959,7 @@ CHECKSUMS
   zeitwerk (2.8.2) sha256=7212a61311083c604184b1ea2574b9aa05cd14f855a0841c06985cabe9181d12
 
 RUBY VERSION
-  ruby 3.4.8p72
+  ruby 4.0.6
 
 BUNDLED WITH
   4.0.15