diff --git a/Gemfile b/Gemfile
index 9bfd1ff1..a4777c71 100644
--- a/Gemfile
+++ b/Gemfile
@@ -71,7 +71,7 @@ group :jekyll_optional_dependencies do
   gem "jekyll-redirect-from"
   gem "kramdown", "~> 1.14"
   gem "mime-types", "~> 3.0"
-  gem "rdoc", RUBY_VERSION >= "2.2.2" ? "~> 6.0" : "~> 5.1"
+  gem "rdoc", "~> 6.0"
   gem "tomlrb", "~> 1.2"
 
   platform :ruby, :mswin, :mingw, :x64_mingw do