diff --git a/ext/psych/lib/psych/deprecated.rb b/ext/psych/lib/psych/deprecated.rb
index 5a96e91154..c0c9abef7a 100644
--- a/ext/psych/lib/psych/deprecated.rb
+++ b/ext/psych/lib/psych/deprecated.rb
@@ -1,3 +1,5 @@
+require 'date'
+
 module Psych
   module DeprecatedMethods # :nodoc:
     attr_accessor :taguri