Article 1870. Underinsurance

(1) The insurer shall be liable for any insured loss up to the sum insured even if the sum insured is less than the value of the property insured at the time when the insured event occurs.
(2) However, the parties may provide that the indemnity owed by the shall be limited to the proportion that the sum insured bears to the actual value of the property at the time of the loss (pro rata indemnity clause). In that case, moreover, mitigation costs, as defined in Article 1863, shall be reimbursed in the same proportion.
(3) A pro rata indemnity clause may be relied upon only if the insurer additionally mentioned about its existence in the text of the insurance policy.