diff --git a/app/models/custom_field.rb b/app/models/custom_field.rb
index 72ac471..6fb0e5a 100644
--- a/app/models/custom_field.rb
+++ b/app/models/custom_field.rb
@@ -279,3 +279,5 @@ class CustomField < ActiveRecord::Base
     end
   end
 end
+
+require_dependency 'redmine/field_format'