In the wake of a recent wave of restatements to correct lease-related accounting errors, the U.S. Securities and Exchange Commission’s chief accountant has issued a letter to a professional accounting group reiterating the rules.

SEC’s Donald Nicolaisen focused the letter on three issues related to lease accounting: depreciation of the costs to improve leased property, how to recognize periods of free or reduced rent, and how to account for landlord incentives to make improvements. Nicolaisen addressed the letter to Robert Keuppers, chairman of the Center for Public Company Audit Firms, which is an arm of the American Institute of Certified Public Accountants.