Various embodiments of a system and method for managing reassignment of units among shipments in a materials handling facility are described. Embodiments may include a system configured to identify a first unit of a particular item that has been picked from inventory of a materials handling facility and assigned to a first shipment. The system may also, from multiple candidate shipments, identify a second shipment that requires a given unit of the particular item in order to become a complete shipment. For each candidate shipment, at least one unit of that shipment may be stored within a defined storage area of a materials handling facility. The system may, in response to identifying both shipments, generate an instruction to reassign the first unit of the particular item from the first shipment to the second shipment in order to transform the second shipment from an incomplete shipment to a complete shipment.