diff --git a/fluentd.gemspec b/fluentd.gemspec
index 74a09c207d..0aa1ab1533 100644
--- a/fluentd.gemspec
+++ b/fluentd.gemspec
@@ -43,15 +43,6 @@ Gem::Specification.new do |gem|
   gem.add_runtime_dependency("async-http", "~> 0.86")
   gem.add_runtime_dependency("json", '>= 2.21')
 
-  if Gem::Version.new(RUBY_VERSION) < Gem::Version.new("4.1")
-    # Fluentd itself no longer uses yajl-ruby, replaced with JSON::ResumableParser.
-    # This dependency is kept temporarily because some third-party plugins `require 'yajl'` without declaring
-    # it in their own gemspec, relying on Fluentd to pull it in.
-    # The version guard exists because yajl-ruby fails to build on Ruby >= 4.1.
-    # We can remove this dependency when retired to support Ruby 4.0 or below.
-    gem.add_runtime_dependency("yajl-ruby", ["~> 1.0"])
-  end
-
   # gems that aren't default gems as of Ruby 3.4
   gem.add_runtime_dependency("base64", ["~> 0.2"])
   gem.add_runtime_dependency("csv", ["~> 3.2"])