Wis. Stat. § 632.08: Mortgage clause.

A provision for payment to a mortgagee or other owner of a security interest in property may be contained in or added by endorsement to any insurance policy protecting against loss or destruction of or damage to property. If the insurance covers real property, any loss not exceeding $500 shall be paid to the insured mortgagor despite the provision, unless the mortgagee is a named insured.