NGRX reducers using the same state object

I have these two reducers:

export function reducer1(state: State = initialState,: Actions1.Actions1);export function reducer2(state: State = initialState,: Actions2.Actions1);

I need those reducers to modify the same state object.

As they will use the same state object, I cannot simply split the state into small pieces to those new reducers use them as this answer says.