diff --git a/Gemfile b/Gemfile
index 1ece4c01..a87f0bd4 100644
--- a/Gemfile
+++ b/Gemfile
@@ -8,3 +8,4 @@ git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }
 ruby '>=2.5.3'
 
 gem 'github-pages', group: :jekyll_plugins
+gem 'webrick'