Context

• node version: 8.1.4
• joi version: 10.6.0
• environment (node, browser): node
• used with (hapi, standalone, ...): standalone
• any other relevant information:

What are you trying to achieve or the steps to reproduce ?

Joi.date().iso().validate('2013').value.toISOString();

Which result you had ?

'1970-01-01T00:00:02.013Z'

What did you expect ?

Same output as new Date('2013').toISOString():

'2013-01-01T00:00:00.000Z'

As far as I can tell, it unexpectedly parses it as a timestamp value.