Compatibilist can accept:

P did A freely = P did A and P was free not to do A.

But for an account of "free not to do" the compatibilist proposes:

P was free not to do A = P's doing A was not compelled by external factors. (Negative Account)

(Stace's Gandhi example P 343b)

Alternatively,

P was free not to do A = If P had chosen not to do A, P would not have done A. (Conditional Account) (Cf. Stace P 344b)