diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
index 2e22d41..86b05be 100644
--- a/.github/workflows/lint.yml
+++ b/.github/workflows/lint.yml
@@ -15,7 +15,7 @@ jobs:
     - name: Set up Ruby
       uses: ruby/setup-ruby@afeafc3d1ab54a631816aba4c914a0081c12ff2f # ruby/setup-ruby@v1 see https://github.com/ruby/setup-ruby/tree/v1
       with:
-        ruby-version: 3.4
+        ruby-version: 4.0
     - name: Install dependencies
       run: bundle install
     - name: Run RuboCop against BASE..HEAD changes
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index b49a811..1379e29 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -8,33 +8,17 @@ jobs:
       fail-fast: false
       matrix:
         ruby-version:
-          - '3.0'
-          - '3.1'
-          - '3.2'
           - '3.3'
           - '3.4'
+          - '4.0'
         gemfile:
-          - gemfiles/Gemfile.rails61
-          - gemfiles/Gemfile.rails70
           - gemfiles/Gemfile.rails71
           - gemfiles/Gemfile.rails72
           - gemfiles/Gemfile.rails80
+          - gemfiles/Gemfile.rails81
         exclude:
-          # rails 6.1 requires ruby < 3.4
-          - ruby-version: '3.4'
-            gemfile: 'gemfiles/Gemfile.rails61'
-          # rails 7.0 requires ruby >= 2.7, < 3.4
-          # https://www.fastruby.io/blog/ruby/rails/versions/compatibility-table.html
-          - ruby-version: '3.4'
-            gemfile: 'gemfiles/Gemfile.rails70'
-          # rails 7.2 requires ruby >= 3.1
-          # https://www.fastruby.io/blog/ruby/rails/versions/compatibility-table.html
-          - ruby-version: '3.0'
-            gemfile: 'gemfiles/Gemfile.rails72'
           # rails 8.0 requires ruby >= 3.2
           # https://www.fastruby.io/blog/ruby/rails/versions/compatibility-table.html
-          - ruby-version: '3.0'
-            gemfile: 'gemfiles/Gemfile.rails80'
           - ruby-version: '3.1'
             gemfile: 'gemfiles/Gemfile.rails80'
 
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 87dffbc..c3a8624 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,6 @@
 ## [Unreleased]
-* no unreleased changes
+### Fixed
+* Support Rails 8.1, Ruby 4.0. Drop support for Ruby 3.2
 
 ## 2.4.3 / 2025-11-07
 ### Fixed
diff --git a/gemfiles/Gemfile.rails61 b/gemfiles/Gemfile.rails61
deleted file mode 100644
index a82521f..0000000
--- a/gemfiles/Gemfile.rails61
+++ /dev/null
@@ -1,15 +0,0 @@
-source 'https://rubygems.org'
-
-gemspec path: '..'
-
-gem 'rails', '~> 6.1.0'
-
-# Rails 6.1 does not support sqlite3 2.x; it specifies gem "sqlite3", "~> 1.4"
-# in lib/active_record/connection_adapters/sqlite3_adapter.rb
-gem 'sqlite3', '~> 1.7'
-
-# Latest concurrent-ruby breaks Rails < 7.1. See https://github.com/rails/rails/issues/54260
-gem 'concurrent-ruby', '1.3.4'
-
-# Rails <= 8.0 does not support minitest 6
-gem 'minitest', '>= 5.11', '< 6.0'
diff --git a/gemfiles/Gemfile.rails70 b/gemfiles/Gemfile.rails70
deleted file mode 100644
index edf0478..0000000
--- a/gemfiles/Gemfile.rails70
+++ /dev/null
@@ -1,15 +0,0 @@
-source 'https://rubygems.org'
-
-gemspec path: '..'
-
-gem 'rails', '~> 7.0.0'
-
-# Rails 7.0 does not support sqlite3 2.x; it specifies gem "sqlite3", "~> 1.4"
-# in lib/active_record/connection_adapters/sqlite3_adapter.rb
-gem 'sqlite3', '~> 1.7'
-
-# Latest concurrent-ruby breaks Rails < 7.1. See https://github.com/rails/rails/issues/54260
-gem 'concurrent-ruby', '1.3.4'
-
-# Rails <= 8.0 does not support minitest 6
-gem 'minitest', '>= 5.11', '< 6.0'
diff --git a/gemfiles/Gemfile.rails81 b/gemfiles/Gemfile.rails81
new file mode 100644
index 0000000..4b958c0
--- /dev/null
+++ b/gemfiles/Gemfile.rails81
@@ -0,0 +1,5 @@
+source 'https://rubygems.org'
+
+gemspec path: '..'
+
+gem 'rails', '~> 8.1.0'
diff --git a/ndr_error.gemspec b/ndr_error.gemspec
index 68d6ec5..87d8a53 100644
--- a/ndr_error.gemspec
+++ b/ndr_error.gemspec
@@ -19,14 +19,9 @@ Gem::Specification.new do |s|
   s.files = Dir['{app,config,db,lib}/**/*', 'CHANGELOG.md', 'CODE_OF_CONDUCT.md',
                 'MIT-LICENSE', 'Rakefile', 'README.md', 'SECURITY.md']
 
-  s.required_ruby_version = '>= 3.0'
+  s.required_ruby_version = '>= 3.3'
 
-  s.add_dependency 'rails', '>= 6.1', '< 8.1'
-
-  # Support rails 6.1 with Ruby 3.1
-  s.add_dependency 'net-imap'
-  s.add_dependency 'net-pop'
-  s.add_dependency 'net-smtp'
+  s.add_dependency 'rails', '>= 7.1', '< 8.2'
 
   s.add_dependency 'will_paginate'
 
@@ -35,23 +30,8 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'pry'
   s.add_development_dependency 'puma'
 
-  # Rails 6.1 and 7.0 do not support sqlite3 2.x; they specify gem "sqlite3", "~> 1.4"
-  # in lib/active_record/connection_adapters/sqlite3_adapter.rb
-  # cf. gemfiles/Gemfile.rails70
   s.add_development_dependency 'sqlite3'
 
-  # Workaround build issue on GitHub Actions with ruby <= 3.1 when installing sass-embedded
-  # gem version 1.81.0: NoMethodError: undefined method `parse' for #<Psych::Parser...>
-  # https://bugs.ruby-lang.org/issues/19371
-  s.add_development_dependency 'psych', '< 5'
-
-  # Workaround build issue on GitHub Actions with ruby <= 3.1 when installing sass-embedded
-  # Versions 1.77.0 and above require ruby >= 3.2 for packaged x86_64-linux binaries
-  # but say they're compatible with ruby 3.1.
-  # 1.76.0 has a bug that was fixed in 1.77.1, which we can't use yet.
-  # https://github.com/sass/dart-sass/issues/2239
-  s.add_development_dependency 'sass-embedded', '~> 1.75.0' if RUBY_VERSION.start_with?('3.1') # rubocop:disable Gemspec/RubyVersionGlobalsUsage
-
   s.add_development_dependency 'mocha'
   s.add_development_dependency 'test-unit', '~> 3.0'