diff --git a/.github/workflows/ubuntu.yml b/.github/workflows/ubuntu.yml
index 6f08a83341..a9e4522628 100644
--- a/.github/workflows/ubuntu.yml
+++ b/.github/workflows/ubuntu.yml
@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby: [ '2.6.x', '2.5.x', '2.4.x', '2.3.x' ]
+        ruby: [ '2.6.x', '2.5.x', '2.4.x' ]
     steps:
     - uses: actions/checkout@master
     - name: Set up Ruby
diff --git a/rdoc.gemspec b/rdoc.gemspec
index ca807a1412..9b274c709a 100644
--- a/rdoc.gemspec
+++ b/rdoc.gemspec
@@ -240,7 +240,7 @@ RDoc includes the +rdoc+ and +ri+ tools for generating and displaying documentat
     TODO.rdoc
   ]
 
-  s.required_ruby_version = Gem::Requirement.new(">= 2.2.2")
+  s.required_ruby_version = Gem::Requirement.new(">= 2.4.0")
   s.rubygems_version = "2.5.2"
   s.required_rubygems_version = Gem::Requirement.new(">= 2.2")
 end