(1) If the work, before acceptance, is destroyed or deteriorates or becomes impracticable as the result of a defect in the materials supplied by the customer or as the result of an instruction given by the customer as to how the work is to be carried out, without a circumstance for which the contractor is responsible contributing to this, then the contractor may demand a portion of the remuneration that corresponds to the work performed and reimbursement of those expenditures not included in the remuneration. The same applies if the contract is cancelled under section 643.
(2) A more extensive liability of the customer for fault remains unaffected.