diff --git a/spec/unit/validators/within_validator_spec.rb b/spec/unit/validators/within_validator_spec.rb
index <HASH>..<HASH> 100644
--- a/spec/unit/validators/within_validator_spec.rb
+++ b/spec/unit/validators/within_validator_spec.rb
@@ -11,6 +11,7 @@ describe 'DataMapper::Validations::WithinValidator' do
         'WithinValidatorClass'
       end
 
+      property :id,   DataMapper::Property::Serial
       property :name, String, :auto_validation => false
     end.new
Make sure the anonymous model defines a primary key