Certificate of Correction

By Eugene T. Perez

Relatively minor mistakes in an issued U.S. patent may be corrected by means of a certificate of correction.1 Correctable mistakes are of three basic types: (a) errors incurred through the fault of the USPTO; (b) errors made by the applicant; and (c) errors regarding the named inventors. If a certificate of correction issues correcting a mistake either on the part of the USPTO or on the part of the applicant, the patent laws and rules provide that the patent, together with the certificate of correction, have the same effect in law as if the patent had issued in the corrected form.

According to the CAFC, there are three types of errors.

The first type involves mistakes that are immediately apparent and leave no doubt as to what is the mistake. This includes, for example, misspellings that leave no doubt as to the word which was intended, e.g., “freane” instead of “frame.” This type of error also extends to clerical errors in which a patentee tries to correct every instance of a particular claim term in prosecution but misses one, leaving a claim that on its face, is nonsensical in light of the specification. The prosecution history would show that the patentee had missed one term and that the proper correction would be to change that term as well. Because an error of this type makes its own correction known to one of ordinary skill in the art, such errors do not raise serious public notice problems and can be corrected by a § 255 certificate.

In contrast, a second type of error includes those typographical mistakes not apparent to the reader at all such as, for example, a mistake resulting in another word that is spelled correctly and reads logically in the context of the sentence.

A third type of error includes those where it is apparent that a mistake has been made, but it is unclear what the mistake is.

An example of an improper Certificate of Correction is found in Central Admixture Pharmacy Serv. Inc. v. Advanced Cardiac Solutions.2In this decision, the patent record did not indicate that “osmolarity” was a mistake or that it should have been corrected to “osmolality”.

An example of when the patent owner should have filed a Certificate of Correction before suing for infringement is found in Group One Ltd. v. Hallmark Cards Inc.3 The USPTO omitted key claim language in the patent due to a printing error. During prosecution, the Examiner added the disputed claim language as a condition for allowance.  The error in the claims should have been corrected with a Certificate of Correction, but the patent owner did not do so.  Thus, the district court could not correct the error since the error was not evident from the face of the patent, and held the patent invalid for indefiniteness.


  1. 35 U.S.C. § 255.
  2. Cent. Admixture Pharm. Servs. v. Advanced Cardiac Solutions, P.C., 482 F.3d 1347, 82 U.S.P.Q.2D (BNA) 1293 (Fed. Cir. 2007).
  3. Group One, Ltd. v. Hallmark Cards, Inc., 407 F.3d 1297, 74 U.S.P.Q.2D (BNA) 1759 (Fed. Cir. 2005).