diff --git a/fluentd.gemspec b/fluentd.gemspec
index 6d5334813b..372d8fa8f6 100644
--- a/fluentd.gemspec
+++ b/fluentd.gemspec
@@ -42,12 +42,12 @@ Gem::Specification.new do |gem|
   gem.add_runtime_dependency("uri", '~> 1.0')
   gem.add_runtime_dependency("async-http", "~> 0.86")
 
-  # It appears io-event >= 1.11.0 are unstable on Windows (confirmed on 1.12.1 or lower).
-  # See https://github.com/fluent/fluentd/issues/5041.
-  gem.add_runtime_dependency("io-event", "< 1.11.0")
-  # io-stream >= 0.8 needs io-event >= 1.12.0, so we need to fix io-stream version as well (confirmed on 0.10.0 or lower).
-  # See https://github.com/socketry/io-stream/issues/8.
-  gem.add_runtime_dependency("io-stream", "< 0.8.0")
+  # # It appears io-event >= 1.11.0 are unstable on Windows (confirmed on 1.12.1 or lower).
+  # # See https://github.com/fluent/fluentd/issues/5041.
+  # gem.add_runtime_dependency("io-event", "< 1.11.0")
+  # # io-stream >= 0.8 needs io-event >= 1.12.0, so we need to fix io-stream version as well (confirmed on 0.10.0 or lower).
+  # # See https://github.com/socketry/io-stream/issues/8.
+  # gem.add_runtime_dependency("io-stream", "< 0.8.0")
 
   # gems that aren't default gems as of Ruby 3.4
   gem.add_runtime_dependency("base64", ["~> 0.2"])
@@ -78,7 +78,7 @@ Gem::Specification.new do |gem|
   # timecop v0.9.9 supports `Process.clock_gettime`. It breaks some tests.
   # (https://github.com/fluent/fluentd/pull/4521)
   gem.add_development_dependency("timecop", ["< 0.9.9"])
-  gem.add_development_dependency("test-unit", ["~> 3.3"])
+  gem.add_development_dependency("test-unit", "= 3.6.8")
   gem.add_development_dependency("test-unit-rr", ["~> 1.0"])
   gem.add_development_dependency("oj", [">= 2.14", "< 4"])
   gem.add_development_dependency("console", "~> 1.30")