Context

• node version: 8~10
• joi version: 14.2.0
• environment: node
• used with: standalone
• any other relevant information: worked with joi@13.0.0, seems to have been introduced with 14.0.0, and still failing with 14.2.0

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

I'm validating extra keys attached to functions (which I reckon, is quite weird from the start 😅).

const joi = require('joi')
const schema = joi.func().keys({
  a: joi.string(),
  b: joi.string()
}).with('a', 'b')

const fct = () => {}
fct.a = 'hello'
// fct.b = 'world!'

joi.assert(fct, schema, 'Error prefix')

Which result you had ?

AssertionError: Invalid segment b in reach path b

see it live

What did you expect ?

Error: Error prefix "a" missing required peer "b"

see it live