diff --git a/Gemfile b/Gemfile
index d648297af0a..90a73623c24 100644
--- a/Gemfile
+++ b/Gemfile
@@ -43,3 +43,5 @@ end
 group :rdoc do
   gem "rdoc", "6.5.0"
 end
+
+gem "psych", "!= 5.1.1" # https://github.com/ruby/psych/issues/655