diff --git a/Gemfile b/Gemfile
index c5f916f..45d3c80 100644
--- a/Gemfile
+++ b/Gemfile
@@ -28,7 +28,7 @@ gem 'jbuilder', '~> 2.7'
 # Reduces boot times through caching; required in config/boot.rb
 gem 'bootsnap', '>= 1.4.2', require: false
 gem 'rails_12factor', group: :production
-
+gem 'psych', '< 4'
 gem 'rack-cors'
 
 group :development, :test do