From ‘Second’ to ‘First:’ Federal Circuit Tackles Obvious Claim Errors

Patent claims must be clear and definite, as they set the boundaries of the patentee’s rights. Occasionally, however, claim language contains errors, such as typographical mistakes or incorrect numbering. Courts possess very limited authority to correct such errors. The United States Court of Appeals for the Federal Circuit has emphasized that judicial correction is appropriate only in rare circumstances, where (1) the error is evident from the face of the patent, and (2) the proposed correction is the sole reasonable interpretation in view of the claim language, specification, and prosecution history. See Group One, Ltd. v. Hallmark Cards, Inc., 407 F.3d 1297, 1303 (Fed. Cir. 2005) and Novo Indus., L.P. v. Micro Molds Corp., 350 F.3d 1348, 1357 (Fed. Cir. 2003).

The recent Canatex decision is the latest pronouncement from the Federal Circuit regarding this demanding standard for judicial correction of claim language, which involved the inadvertent use of “second” instead of “first” in a patent claim. On November 12, 2025, the Federal Circuit issued a significant opinion in Canatex Completion Solutions, Inc. v. Wellmatics, LLC, clarifying the circumstances under which courts may judicially correct errors in patent claim language. The Federal Circuit reversed the district court’s invalidation of Canatex’s patent claims for indefiniteness, finding that the error in the claim language was both obvious and correctable.

While the standard for judicial correction was most recently reaffirmed in Canatex, its application is not always straightforward. For example, in Chef Am., Inc. v. Lamb-Weston, Inc., 358 F.3d 1371 (Fed. Cir. 2004), the Federal Circuit reached the opposite conclusion, refusing to correct a claim error even when the literal language led to an unworkable outcome. Considering these decisions side by side provides important guidance for patent owners, practitioners, and litigants regarding the boundaries and demanding standard for judicial correction of claim language.

Canatex: Judicial Correction of Claim Language

The dispute in Canatex centered on the phrase “the connection profile of the second part” in Canatex’s U.S. Patent No. 10,794,122. The defendant asserted the claim term lacked an antecedent basis and was inconsistent with the claimed invention. Canatex asserted that the recitation of “the second” was a clerical error and that a person skilled in the art would recognize the intended meaning as “the connection profile of the first part.” The district court disagreed, finding the error was not sufficiently evident and the correction was not straightforward.

On appeal, the Federal Circuit reversed while emphasizing the stringent standard for judicial correction: the error must be obvious from the face of the patent, and the correction must be the only reasonable interpretation supported by the intrinsic evidence (meaning the contents of the patent itself, including the claim language, the specification, and the record of communications with the U.S. Patent and Trademark Office during the application process). The court found that the claim language, specification, and figures all clearly indicated that the “connection profile” referred to the first part, not the second part, and no alternative correction was supported by the patent’s disclosure or prosecution history. Accordingly, the court held that the error was obvious and minor, and judicial correction to “the connection profile of the first part” was appropriate. This decision reinforces that courts may correct only obvious and minor errors in claim language when the correction is clear and undisputed by the intrinsic evidence.

Notably, shortly after the district court entered its final judgment and Canatex appealed, Canatex sought administrative correction of the disputed claim language from the USPTO under 35 U.S.C. § 255. The Office denied the request in March 2025, stating that the requested correction “sought to change the scope of the patented claims” without further explanation. This denial highlights the difference between administrative corrections and the circumstances in which judicial correction may apply, demonstrating that judicial correction may be required when administrative correction is unavailable.

It is important to note that corrections through a certificate of correction under 35 U.S.C. § 255 are only effective for actions “thereafter arising.” A certificate of correction issued after commencement of litigation does not retroactively cure claim defects for acts of infringement before its issuance. As a result, damages before the correction are unavailable. This limiting effect of administrative correction underscores the importance of identifying and correcting obvious errors in claim language before litigation begins given the uncertainty of correction by a district court.

Comparing Federal Circuit Approaches: Canatex and Chef America

The demanding standard for judicial correction, as restated in Canatex, might appear straightforward: courts may fix claim language only when the error is evident on the face of the patent and the proposed correction is the sole reasonable interpretation based on the claims, specification, and prosecution history. In practice, however, the Federal Circuit’s decisions reveal uncertainty over exactly when judicial correction is proper, notably in the contrast between the Canatex and Chef America cases.

In contrast to the outcome in Canatex, Chef America involved what appeared to be a similarly evident error: the claim required heating dough “to” temperatures that would render the product unusable. The issue was whether the claim required the oven or the dough to be heated to a certain temperature or the dough, when the claim as written required the dough to be heated to a specific temperature range. Despite the practical impossibility (and only one sensible interpretation), the court refused to correct the claim, emphasizing the public notice function and the principle that courts cannot redraft or rewrite clear claim language, even to save the claim from invalidity. The court pointed to the prosecution history, which indicated “to” was chosen intentionally, and concluded that “[w]here, as here, claims are susceptible to only one reasonable construction and that interpretation results in a nonsensical construction of the claim as a whole, the claim must be invalidated.”

The prosecution history in Chef America played an important role in that case outcome: the presence of deliberate language choices can make or break a motion for judicial correction. In Canatex, the Federal Circuit distinguished Chef America by emphasizing that, in Chef America, the prosecution history confirmed the drafter’s intentional selection of “to” rather than “at,” leaving no basis for judicial correction, even though the claimed process was inoperable as written. In Canatex, by contrast, the specification and figures injected no ambiguity or deliberate attempt to substitute “first” for “second” by the patentee. Since the prosecution history provided no evidence of a deliberate choice in claim drafting, every person of skill in the art would recognize the clerical nature of the error.

Chef America stands as a stark reminder that courts cannot redraft or rewrite claims to rescue them from invalidity. The divergence between Canatex and Chef America illustrates the fine line courts must walk: a correction may be made for a clear clerical mistake when the intrinsic evidence compels only one outcome, but even an obvious error will stand if the claim language and the intrinsic record suggest a purposeful choice in claim language.

Practical Implications and Guidance

Canatex means that judicial correction should be viewed as a rare exception, triggered only when a clear error in claim language is obvious to a person of skill in the art and the intrinsic record compels a single correction. Patent drafters should meticulously review claims before filing to catch even minor errors, which may be particularly acute when claims are rewritten from dependent form to independent form, or when examiners suggest claim amendments. Courts generally will not rescue claim errors unless correction is clear and the claim is subject to only a single possible correction. In practice, a careful review of allowed claims remains the best practice.