35 U.S.C. § 288 : US Code - Section 288: Action for infringement of a patent containing an invalid claim

Search 35 U.S.C. § 288 : US Code - Section 288: Action for infringement of a patent containing an invalid claim

Whenever, without deceptive intention, a claim of a patent is
invalid, an action may be maintained for the infringement of a
claim of the patent which may be valid. The patentee shall recover
no costs unless a disclaimer of the invalid claim has been entered
at the Patent and Trademark Office before the commencement of the
suit.