[Agda] order inside a mutual block is relevant?

[David Leduc]

I was expecting that the order of definitions inside a mutual block
was irrelevant.
The definition below is accepted by the type checker.
But if I change the order of definitions of x and t, then it is rejected.
Isn't it odd?

module test where

open import Data.Bool

mutual

  t : Set
  t = Bool

  x : t
  x = true