diff --git a/.travis.yml b/.travis.yml
index 1e243481bae..c091601d3f4 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -29,7 +29,7 @@
 language: ruby
 
 rvm:
-  - 2.6.5
+  - 2.6.6
 
 sudo: required
 dist: xenial
diff --git a/Gemfile b/Gemfile
index 52d1fc2b21f..2c788bf5a3c 100644
--- a/Gemfile
+++ b/Gemfile
@@ -28,7 +28,7 @@
 
 source 'https://rubygems.org'
 
-ruby '~> 2.6.5'
+ruby '~> 2.6.6'
 
 gem 'actionpack-xml_parser', '~> 2.0.0'
 gem 'activemodel-serializers-xml', '~> 1.0.1'
diff --git a/Gemfile.lock b/Gemfile.lock
index 2e47b4fc049..f9eb953f2fa 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1119,7 +1119,7 @@ DEPENDENCIES
   with_advisory_lock (~> 4.6.0)
 
 RUBY VERSION
-   ruby 2.6.5p114
+   ruby 2.6.6p146
 
 BUNDLED WITH
    2.1.4
diff --git a/docs/development/development-environment-osx/README.md b/docs/development/development-environment-osx/README.md
index 94112eaa262..1e442ea2c11 100644
--- a/docs/development/development-environment-osx/README.md
+++ b/docs/development/development-environment-osx/README.md
@@ -32,20 +32,20 @@ $ rbenv init
 **Installing ruby-2.6**
 
 With both installed, we can now install the actual ruby version 2.6. You can check available ruby versions with `rbenv install --list`.
-At the time of this writing, the latest stable version is `2.6.5`, which we also require.
+At the time of this writing, the latest stable version is `2.6.6`, which we also require.
 
 We suggest you install the version we require in the [Gemfile](https://github.com/opf/openproject/blob/dev/Gemfile). Search for the `ruby '~> X.Y.Z'` line
 and install that version.
 
 ```bash
 # Install the required version as read from the Gemfile
-rbenv install 2.6.5
+rbenv install 2.6.6
 ```
 
 This might take a while depending on whether ruby is built from source. After it is complete, you need to tell rbenv to globally activate this version
 
 ```bash
-rbenv global 2.6.5
+rbenv global 2.6.6
 ```
 
 You also need to install [bundler](https://github.com/bundler/bundler/), the ruby gem bundler.
@@ -110,7 +110,7 @@ You should now have an active ruby and node installation. Verify that it works w
 
 ```bash
 $ ruby --version
-ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-darwin16]
+ruby 2.6.6p114 (2019-10-01 revision 67812) [x86_64-darwin16]
 
 $ bundler --version
 Bundler version 2.0.2
diff --git a/docs/development/development-environment-ubuntu/README.md b/docs/development/development-environment-ubuntu/README.md
index 42854c6bdd7..71037a67081 100644
--- a/docs/development/development-environment-ubuntu/README.md
+++ b/docs/development/development-environment-ubuntu/README.md
@@ -54,20 +54,20 @@ git clone https://github.com/rbenv/ruby-build.git ~/.rbenv/plugins/ruby-build
 **Installing ruby-2.6**
 
 With both installed, we can now install the actual ruby version 2.6. You can check available ruby versions with `rbenv install --list`.
-At the time of this writing, the latest stable version is `2.6.5`, which we also require.
+At the time of this writing, the latest stable version is `2.6.6`, which we also require.
 
 We suggest you install the version we require in the [Gemfile](https://github.com/opf/openproject/blob/dev/Gemfile). Search for the `ruby '~> X.Y.Z'` line
 and install that version.
 
 ```bash
 # Install the required version as read from the Gemfile
-rbenv install 2.6.5
+rbenv install 2.6.6
 ```
 
 This might take a while depending on whether ruby is built from source. After it is complete, you need to tell rbenv to globally activate this version
 
 ```bash
-rbenv global 2.6.5
+rbenv global 2.6.6
 rbenv rehash
 ```
 
@@ -149,7 +149,7 @@ You should now have an active ruby and node installation. Verify that it works w
 
 ```bash
 ruby --version
-ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-linux]
+ruby 2.6.6p114 (2019-10-01 revision 67812) [x86_64-linux]
 
 bundler --version
 Bundler version 2.0.2