diff --git a/Gemfile b/Gemfile
index cf9c01808..27988418c 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,5 +1,6 @@
 source 'https://rubygems.org'
 
+ruby '>= 2.3.0', '< 2.7.0'
 gem "bundler", ">= 1.5.0"
 
 gem "rails", "5.2.4.1"
diff --git a/doc/INSTALL b/doc/INSTALL
index 2213887fa..25a151641 100644
--- a/doc/INSTALL
+++ b/doc/INSTALL
@@ -7,7 +7,7 @@ http://www.redmine.org/
 
 == Requirements
 
-* Ruby >= 2.3
+* Ruby 2.3, 2.4, 2.5, 2.6
 * RubyGems
 * Bundler >= 1.5.0