diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 74b096c..cd1401f 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -21,6 +21,7 @@ jobs:
           - '3.1.3'
           - '3.2.1'
           - '3.3.0'
+          - '4.0.1'
 
     steps:
     - uses: actions/checkout@v3
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1ab1cb2..a97d8f2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 ## [Unreleased]
 
+## [1.5.1] - 2026-01-13
+
+- Ruby 4: Gem will no longer refuse to load.
+
 ## [1.5.0] - 2025-04-25
 
 - Added back `Bignum` as an alias for `Integer`.
diff --git a/Gemfile.lock b/Gemfile.lock
index 60bbc31..547da1b 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    ruby3-backward-compatibility (1.5.0)
+    ruby3-backward-compatibility (1.5.1)
 
 GEM
   remote: https://rubygems.org/
@@ -11,7 +11,7 @@ GEM
     diff-lcs (1.5.0)
     i18n (1.12.0)
       concurrent-ruby (~> 1.0)
-    rake (13.0.6)
+    rake (13.3.1)
     rspec (3.11.0)
       rspec-core (~> 3.11.0)
       rspec-expectations (~> 3.11.0)
@@ -35,6 +35,3 @@ DEPENDENCIES
   rake (~> 13.0)
   rspec (~> 3.0)
   ruby3-backward-compatibility!
-
-BUNDLED WITH
-   2.3.22
diff --git a/lib/ruby3_backward_compatibility/version.rb b/lib/ruby3_backward_compatibility/version.rb
index 7f12d8b..9bf2a6d 100644
--- a/lib/ruby3_backward_compatibility/version.rb
+++ b/lib/ruby3_backward_compatibility/version.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module Ruby3BackwardCompatibility
-  VERSION = '1.5.0'
+  VERSION = '1.5.1'
 end