diff --git a/.github/Dockerfile.base b/.github/Dockerfile.base
index 5fae1efe..39557d77 100644
--- a/.github/Dockerfile.base
+++ b/.github/Dockerfile.base
@@ -3,7 +3,7 @@
 # call this from rails root: podman build -t mapforge-base -f .github/Dockerfile.base .
 
 # Make sure RUBY_VERSION matches the Ruby version in .ruby-version and Gemfile
-ARG RUBY_VERSION=3.4.5
+ARG RUBY_VERSION=4.0.0
 FROM registry.docker.com/library/ruby:$RUBY_VERSION-slim as base
 
 LABEL org.opencontainers.image.source="https://github.com/mapforge-org/mapforge"
diff --git a/.rubocop.yml b/.rubocop.yml
index 437af5cd..e8f37347 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -5,7 +5,7 @@ inherit_gem:
 inherit_from: .rubocop_todo.yml
 
 AllCops:
-  TargetRubyVersion: 3.4
+  TargetRubyVersion: 4.0
   DisplayCopNames: true
   DisplayStyleGuide: true
   ExtraDetails: true
diff --git a/.ruby-version b/.ruby-version
index 4f5e6973..fcdb2e10 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-3.4.5
+4.0.0
diff --git a/Gemfile b/Gemfile
index 25ab22ad..b89f2bd0 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,5 +1,5 @@
 source "https://rubygems.org"
-ruby "3.4.5"
+ruby "4.0.0"
 
 gem "rails"
 
@@ -58,7 +58,8 @@ gem "rszr"
 gem "rgeo"
 gem "rgeo-geojson"
 gem "rgeo-proj4"
-gem "gpx"
+gem "gpx", git: "https://github.com/digitaltom/gpx"
+gem "csv" # required by gpx, and not part of Ruby 4.0 standard lib anymore
 # resolving request IP addresses to coordinates
 gem "maxminddb"
 
diff --git a/Gemfile.lock b/Gemfile.lock
index 4cbd9bf1..daca775a 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,3 +1,12 @@
+GIT
+  remote: https://github.com/digitaltom/gpx
+  revision: 2c2dd533da977ce2a45f77a625a8974cf653dd40
+  specs:
+    gpx (1.2.1)
+      csv
+      nokogiri (~> 1.7)
+      rake
+
 GIT
   remote: https://github.com/ruby/net-pop.git
   revision: 30d89b359c940610d84ecd1fed0dba4003508fde
@@ -125,7 +134,7 @@ GEM
     connection_pool (3.0.2)
     cookiejar (0.3.4)
     crass (1.0.6)
-    csv (3.3.3)
+    csv (3.3.5)
     database_cleaner-core (2.0.1)
     database_cleaner-mongoid (2.0.1)
       database_cleaner-core (~> 2.0.0)
@@ -220,10 +229,6 @@ GEM
       i18n (>= 0.7)
       multi_json
       request_store (>= 1.0)
-    gpx (1.2.1)
-      csv
-      nokogiri (~> 1.7)
-      rake
     haml (7.1.0)
       temple (>= 0.8.2)
       thor
@@ -280,6 +285,7 @@ GEM
     mini_magick (5.3.1)
       logger
     mini_mime (1.1.5)
+    mini_portile2 (2.8.9)
     minitest (6.0.0)
       prism (~> 1.5)
     mongo (2.21.3)
@@ -319,6 +325,9 @@ GEM
     net-smtp (0.5.1)
       net-protocol
     nio4r (2.7.5)
+    nokogiri (1.18.10)
+      mini_portile2 (~> 2.8.2)
+      racc (~> 1.4)
     nokogiri (1.18.10-x86_64-linux-gnu)
       racc (~> 1.4)
     oauth2 (2.0.9)
@@ -520,7 +529,7 @@ GEM
       rubocop-ast (>= 1.44.0, < 2.0)
     ruby-next-core (1.1.2)
     ruby-progressbar (1.13.0)
-    ruby_parser (3.21.1)
+    ruby_parser (3.22.0)
       racc (~> 1.5)
       sexp_processor (~> 4.16)
     rubycritic (4.11.0)
@@ -543,7 +552,7 @@ GEM
       rexml (~> 3.2, >= 3.2.5)
       rubyzip (>= 1.2.2, < 4.0)
       websocket (~> 1.0)
-    sexp_processor (4.17.4)
+    sexp_processor (4.17.5)
     simplecov (0.22.0)
       docile (~> 1.1)
       simplecov-html (~> 0.11)
@@ -629,13 +638,14 @@ DEPENDENCIES
   byebug
   capybara
   capybara-screenshot
+  csv
   database_cleaner-mongoid
   debug
   dotenv-rails
   dragonfly
   factory_bot_rails
   gon
-  gpx
+  gpx!
   haml
   hotwire-spark
   importmap-rails
@@ -690,7 +700,7 @@ DEPENDENCIES
   yabeda-rails
 
 RUBY VERSION
-   ruby 3.4.5
+  ruby 4.0.0p0
 
 BUNDLED WITH
-   2.7.1
+  4.0.3