diff --git a/Gemfile b/Gemfile
index e075c6c..fea45ca 100644
--- a/Gemfile
+++ b/Gemfile
@@ -4,7 +4,7 @@ gemspec
 
 group :development do
   gem "countloc", "~> 0.4"
-  gem "yard",      "~> 0.8"
+  gem "yard",      "~> 0.9", ">= 0.9.20"
   gem "pry"
   gem "pry-stack_explorer"
   gem "pry-byebug"