Accumulated Depreciation for existing Parter when filing 754 step up in basis

I have an LLC with 50/50 partners.  One of the partners sold his 50% interest.  I am doing a 754 step up in basis.  I know that the original partner can only take depreciation on 50% of the original cost of the building.  The original building has a cost net of land of $170,000 and accumulated depreciation of $20,807.  When I calculate his depreciation for this year his cost would be $85,000 but do I allocate accumulated depreciation of $10,403.50 or the full $20,807?  I read someplace that all prior depreciation stands as it was, which to me means you list it all, but that does not make sense to me.