y-or-n-p does not add "(y or n)"

[Juanma Barranquero]

Didn't this

  2010-09-12  Stefan Monnier  <address@hidden>

          * subr.el (y-or-n-p): New function, moved from src/fns.c.
Use read-key.

forgot to implement this part?

  The argument PROMPT is the string to display to ask the question.
  It should end in a space; `y-or-n-p' adds `(y or n) ' to it.

At least,

  M-: (y-or-n-p "My question ") <RET>

does not add "(y or n)" in my tests.

    Juanma