Accounting for 401k profit sharing contribution

Accrual S-Corp makes 401k profit sharing contribution in 2018 for 2017 before the due date of the return.
404(a)(6) the deduction is taken in 2017.
Bookkeeper post transaction in 2018 so it doesn't show as a liability on the 2017 books.
M-1 adjustment or go back and post a liability in 2017?

Post the liability

Thanks Cap'n.

Yep....why make an excessive M-1? What CaptCook said. The trade of "bookkeeper" has declined over the years to cash basis...fewer and fewer really understand accrual accounting.

The trade of "bookkeeper"

I believe "Quickbooks data entry technician" is a better description for most of the "so called" bookkeepers I encounter nowadays.