diff --git a/benchmarks/fluentd/Gemfile b/benchmarks/fluentd/Gemfile
index 3f7549a1..cf67c2e8 100644
--- a/benchmarks/fluentd/Gemfile
+++ b/benchmarks/fluentd/Gemfile
@@ -2,4 +2,3 @@ source 'https://rubygems.org'
 git_source(:github) { |repo| "https://github.com/#{repo}.git" }
 
 gem 'fluentd'
-gem 'cool.io', github: 'k0kubun/cool.io', branch: 'ruby-3-3'
diff --git a/benchmarks/fluentd/Gemfile.lock b/benchmarks/fluentd/Gemfile.lock
index 1dda7d59..5d629396 100644
--- a/benchmarks/fluentd/Gemfile.lock
+++ b/benchmarks/fluentd/Gemfile.lock
@@ -1,14 +1,8 @@
-GIT
-  remote: https://github.com/k0kubun/cool.io.git
-  revision: 61e3caf8b961fb1a4d46b367eb58ebcddb45da4a
-  branch: ruby-3-3
-  specs:
-    cool.io (1.7.1)
-
 GEM
   remote: https://rubygems.org/
   specs:
     concurrent-ruby (1.2.2)
+    cool.io (1.8.0)
     fluentd (1.16.2)
       bundler
       cool.io (>= 1.4.5, < 2.0.0)
@@ -39,7 +33,6 @@ PLATFORMS
   x86_64-linux
 
 DEPENDENCIES
-  cool.io!
   fluentd
 
 BUNDLED WITH