diff --git a/spec/data_spec.rb b/spec/data_spec.rb
index 2bd86a9..0cb7d12 100644
--- a/spec/data_spec.rb
+++ b/spec/data_spec.rb
@@ -15,7 +15,7 @@ class Company < Types::Data
       attribute :email, String[/.+@.+/]
     end
     attribute :company, Company
-    attribute :books, Array do
+    attribute :books, Array.default([].freeze) do
       attribute :isbn, String
     end