diff --git a/Gemfile.lock b/Gemfile.lock
index 275544c..d9ca07c 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -34,7 +34,7 @@ GEM
     parallel (1.20.1)
     parser (3.1.2.0)
       ast (~> 2.4.1)
-    power_assert (2.0.1)
+    power_assert (2.0.3)
     public_suffix (4.0.7)
     rainbow (3.1.1)
     rake (13.0.6)
@@ -62,7 +62,7 @@ GEM
     td-client (1.0.8)
       httpclient (>= 2.7)
       msgpack (>= 0.5.6, < 2)
-    test-unit (3.5.5)
+    test-unit (3.6.0)
       power_assert
     test-unit-rr (1.0.5)
       rr (>= 1.1.1)
@@ -87,7 +87,7 @@ DEPENDENCIES
   rake (>= 0.9.2)
   rubocop
   rubocop-rake
-  test-unit (~> 3.5.3)
+  test-unit (~> 3.6.0)
   test-unit-rr (~> 1.0.5)
   webmock (~> 3.18.1)
 
diff --git a/fluent-plugin-td.gemspec b/fluent-plugin-td.gemspec
index ef5d529..31a378c 100644
--- a/fluent-plugin-td.gemspec
+++ b/fluent-plugin-td.gemspec
@@ -20,7 +20,7 @@ Gem::Specification.new do |gem|
   gem.add_development_dependency 'rake', '>= 0.9.2'
   gem.add_development_dependency 'rubocop'
   gem.add_development_dependency 'rubocop-rake'
-  gem.add_development_dependency 'test-unit', '~> 3.5.3'
+  gem.add_development_dependency 'test-unit', '~> 3.6.0'
   gem.add_development_dependency 'test-unit-rr', '~> 1.0.5'
   gem.add_development_dependency 'webmock', '~> 3.18.1'
 end