SU 5789 is a wall that forms the northern boundary of room 21. It was likely built at a later date, after the building had ceased to serve its original purpose and was therefore meant to aid in the reuse of this portion of the building. Since there is no facing on the northern side, it appears to have been built contraterra after the abandonment of the area just to the north. The western extent of its southern face contains a fragment of marble revetment indicating cotemporary use with the later phase of room 21.