Context

• node version: 6.x
• joi version: 10.4.1
• environment (node, browser): node
• used with (hapi, standalone, ...): standalone
• any other relevant information:

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

const schema = Joi.object({
    a: Joi.number(),
    b: Joi.number(),
    c: Joi.number()
        .when('a', { is: 1, otherwise: Joi.number().min(1) })
        .when('b', { is: 1, then: Joi.number().min(1) })
})

schema.validate({
    a: 1,
    b: 1,
    c: 0
});

Which result you had ?

{ error: null, value: { a: 1, b: 1, c: 0 } }

What did you expect ?

An error with child "c" fails because ["c" must be larger than or equal to 1]