diff --git a/Gemfile b/Gemfile
index d89048a..af1f9f6 100644
--- a/Gemfile
+++ b/Gemfile
@@ -15,7 +15,7 @@ group :development, :test do
   gem 'listen', '~> 3.1', '>= 3.5.0'
   gem 'minitest', '~> 5.14', '>= 5.14.2'
   gem 'rack', '~> 3.0'
-  gem 'rdoc', '~> 6.3', '>= 5.1.0'
+  gem 'rdoc', '~> 6.6'
   gem 'rspec', '~> 3.7', '>= 3.7.0'
   gem 'rubocop', '~> 1.59', '>= 0.52.1'
   gem 'rubocop-minitest'
diff --git a/Gemfile.lock b/Gemfile.lock
index cbd675e..691680b 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -97,7 +97,7 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rdoc (6.6.2)
+    rdoc (6.6.3.1)
       psych (>= 4.0.0)
     regexp_parser (2.8.3)
     rexml (3.2.6)
@@ -179,7 +179,7 @@ DEPENDENCIES
   listen (~> 3.1, >= 3.5.0)
   minitest (~> 5.14, >= 5.14.2)
   rack (~> 3.0)
-  rdoc (~> 6.3, >= 5.1.0)
+  rdoc (~> 6.6)
   rspec (~> 3.7, >= 3.7.0)
   rubocop (~> 1.59, >= 0.52.1)
   rubocop-minitest