When a Missing Coinventor Cannot Be Found: Federal Circuit Affirms Invalidity of Patents for Omission of an Unreachable Inventor in Fortress Iron, LP v. Digger Specialties, Inc.
Introduction
On April 2, 2026, the United States Court of Appeals for the Federal Circuit issued its opinion in Fortress Iron, LP v. Digger Specialties, Inc., No. 2024-2313, a case of first impression addressing a critical question under 35 U.S.C. § 256(b): What happens when a patent owner acknowledges that an individual is an omitted coinventor, but cannot locate that coinventor to provide the notice and hearing that § 256(b) requires before a court may order correction of inventorship?
The answer, the Federal Circuit held, is stark: the patent is invalid and cannot be saved. In an opinion authored by Judge Lourie, joined by Judge Hughes and visiting Chief District Judge Kleeh, the Court affirmed the district court’s grant of summary judgment of invalidity and its denial of the patent owner’s motion to correct inventorship. The panel held that an omitted coinventor is a “party concerned” under § 256(b), that notice and an opportunity to be heard are statutory prerequisites, not mere formalities, and that a patent that incorrectly lists its inventors and cannot be corrected under § 256 is invalid.
As we will discuss below, the case underscores the critical importance of rigorously documenting inventorship, maintaining contact with all contributors, and proactively managing inventorship determinations before patent applications are filed.
Patents at Issue
The two patents at issue in this appeal are: U.S. Patent No. 9,790,707 (“the ’707 patent”) and U.S. Patent No. 10,883,290 (“the ’290 patent”).
Both patents were originally assigned to Fortress Iron, LP (“Fortress”) and were directed to vertical cable railing panel technology. Initially, only Matthew Sherstad (Fortress’s owner) and Kevin Burt (a Fortress employee) were named as inventors. During the course of the underlying infringement litigation, it was acknowledged that two employees of Quan Zhou Yoddex Building Material Co., Ltd. (“YD”), Hua-Ping Huang and Alfonso (Shih-Te) Lin, were also coinventors. Lin was successfully added as a coinventor under § 256(a). Huang, however, could not be located, and his addition was never accomplished.
What Is the Technology?
The patents at issue relate to pre-assembled vertical cable railing panels used in the construction of outdoor living spaces, including decks, balconies, and stairways. In the railing and fencing industry, cable railing systems have become popular for their clean, modern aesthetic and relatively unobstructed sightlines compared to traditional picket or baluster railings.
Conventional cable railing systems, however, typically require extensive on-site assembly. Individual cables must be threaded through posts, tensioned, and secured one by one—a process that is labor-intensive, time-consuming, and demands specialized tools and expertise. Moreover, maintaining proper and uniform cable tension over time can be challenging, and exposed hardware (turnbuckles, threaded fittings, and the like) can be both aesthetically undesirable and vulnerable to tampering.
The inventive concept underlying the ’707 and ’290 patents was a pre-assembled vertical cable railing panel, a modular railing unit in which vertical cables are pre-installed and pre-tensioned within a top rail and a bottom rail before the panel reaches the installation site. The pre-assembled panel approach dramatically simplifies installation: rather than threading and tensioning individual cables in the field, the installer receives a complete panel that can be mounted between posts with minimal on-site labor.
In March 2013, Fortress’s owner Matthew Sherstad conceived the idea for a vertical cable railing that could be purchased as a pre-assembled panel. Kevin Burt produced initial design sketches. Sherstad and Burt worked with YD, a Chinese quality control liaison company, to develop a prototype. The prototype, however, encountered a specific technical problem: the cables rotated during tensioning, which would compromise the integrity, safety, and aesthetics of the railing. YD employees Hua-Ping Huang and Alfonso Lin suggested design changes to address this cable tensioning problem. Those suggestions were incorporated into the final design, which thus reflected the combined contributions of Sherstad, Burt, Huang, and Lin.
35 U.S.C. § 256
35 U.S.C. § 256 provides:
(a) Correction.––Whenever through error a person is named in an issued patent as the inventor, or through error an inventor is not named in an is-sued patent, the Director may, on application of all the parties and assignees, with proof of the facts and such other requirements as may be imposed, issue a certificate correcting such error.
(b) Patent Valid if Error Corrected.––The error of omitting inventors or naming persons who are not inventors shall not invalidate the patent in which such error occurred if it can be corrected as pro-vided in this section. The court before which such matter is called in question may order correction of the patent on notice and hearing of all parties concerned and the Director shall issue a certificate accordingly.
Procedural History
The procedural history of this case is essential to understanding the Federal Circuit’s analysis.
January 2021: Fortress filed suit against Digger Specialties, Inc. (“DSI”) in the United States District Court for the Northern District of Indiana (No. 3:21-cv-00014-CCB, Judge Cristal C. Brisco), alleging infringement of the ’707 and ’290 patents.
Discovery of Coinventors: During the course of the litigation, DSI learned that Alfonso Lin and Hua-Ping Huang of YD had contributed to the invention. Fortress acknowledged that both Lin and Huang were coinventors.
Correction Under § 256(a): Fortress located Lin and successfully added him as a coinventor to both patents using the administrative procedure set forth in 35 U.S.C. § 256(a), which permits the Director of the USPTO to issue a certificate correcting inventorship “on application of all the parties and assignees, with proof of the facts.”
Inability to Locate Huang: Huang’s employment at YD ended in 2016, and he did not provide his contact information to YD or Fortress upon departure. Fortress was unable to locate Huang and therefore could not add him as a coinventor under § 256(a). Before the district court, Fortress conceded that it could not satisfy § 256(a)’s requirements with respect to Huang.
Cross-Motions for Summary Judgment: The parties filed cross-motions. Fortress moved for partial summary judgment seeking inventorship correction by court order under § 256(b). DSI opposed that motion and moved for summary judgment of invalidity based on the omission of Huang as a coinventor.
District Court Decision: The district court denied Fortress’s motion to the extent it declined to order correction of the patents, concluding that Huang was a “party concerned” under § 256(b) who was entitled to notice and an opportunity to be heard before any court-ordered correction. Because Fortress could not provide that notice, the court held that § 256(b) could not be used to correct the patents. The court then granted DSI’s motion for summary judgment, holding both patents invalid for omission of an inventor. Fortress Iron L.P. v. Digger Specialties, Inc., 748 F. Supp. 3d 614, 621 (N.D. Ind. 2024).
Appeal: Fortress appealed to the Federal Circuit. The Court had jurisdiction under 28 U.S.C. § 1295(a)(1).
Key Issues on Appeal
The Federal Circuit identified this as a “case of first impression,” with counsel for both parties agreeing at oral argument that no prior case addressed these precise facts. The two key issues on appeal were:
Issue 1: Did the district court err in denying Fortress’s partial summary judgment motion to correct inventorship under 35 U.S.C. § 256(b)?
Specifically, this issue turned on whether Hua-Ping Huang, an acknowledged but unreachable omitted coinventor, qualified as a “party concerned” under § 256(b), and whether the statute’s notice and hearing requirements were mandatory prerequisites that could not be waived or dispensed with when a coinventor could not be located.
Issue 2: Did the district court err in granting DSI’s motion for summary judgment of invalidity based on the omission of Huang as a coinventor?
This issue required the court to address whether a patent that omits an inventor is invalid when the error cannot be corrected under § 256, and specifically whether the statutory framework requires that all inventors be named on a patent for it to be valid.
Findings and Holdings of the Federal Circuit
The Federal Circuit affirmed the district court on both issues. The opinion, while relatively concise, addresses multiple layers of statutory interpretation and rejects several arguments advanced by Fortress.
Huang Is a “Party Concerned” Under § 256(b)
The Court began by emphasizing the centrality of inventors in the patent system, stating: “Inventors occupy the central role in the patent process. They are where it all begins, even if they eventually assign their interests to others, such as employers. Thus, their explicit references in the statutory framework cannot be taken lightly.”
Relying on Chou v. University of Chicago, 254 F.3d 1347, 1357 (Fed. Cir. 2001), the Court held that Huang, as an agreed-upon omitted coinventor, is a “party concerned” under § 256(b) and must be given notice and an opportunity for hearing before a court may order correction of inventorship.
The court then rejected each of Fortress’s counterarguments in turn:
(1) The “Due Process” / Adverse Interest Argument. Fortress argued that “party concerned” should be read through a due process lens, such that only a person with an economic interest that may be adversely affected qualifies. Under this theory, adding Huang as a coinventor would benefit him, not harm him, so he should not be treated as a “party concerned.” The Court rejected this argument on multiple grounds. First, it noted that neither the parties nor the court could know whether Huang would benefit or be adversely affected by being listed as a coinventor. Second, and more fundamentally, the Court refused to rewrite the statutory text, stating that “to conflate a ‘party concerned’ with those with potentially adversely affected property interests would be to rewrite the language of the statute from ‘party concerned’ to ‘those with an economic interest that may be adversely affected.’” The Court emphasized that inventorship carries legal, financial, and ownership consequences that an inventor has a right to contest, citing 35 U.S.C. § 262 (each joint owner may practice the invention without the consent of and without accounting to other owners) and Ethicon, Inc. v. U.S. Surgical Corp., 135 F.3d 1456, 1465 (Fed. Cir. 1998) (each coinventor presumptively owns a pro rata undivided interest in the entire patent).
(2) The Constitutional Standing Argument. Fortress argued that Huang is not a “party concerned” because he would lack constitutional standing to name himself a coinventor. The Court disposed of this argument by reference to Chou, which held that constitutional standing and “party concerned” status under § 256(b) are distinct issues with different requirements. A person can be a “party concerned” without necessarily having Article III standing to invoke § 256(b) on their own behalf.
(3) The “Savings Provision” / Broad Construction Argument. Fortress argued that § 256 should be construed “broadly and permissively” because of its status as a “savings provision”. While the Court acknowledged that § 256 has been characterized as a savings provision (citing Pannu v. Iolab Corp., 155 F.3d 1344, 1350 (Fed. Cir. 1998)), it held that the provision “is a ‘savings provision’ only to the extent that its statutory requirements are met.” The statute expressly states that a patent is not invalidated for inventorship error “if it can be corrected as provided in this section”. Because Fortress could not satisfy the notice and hearing prerequisite, the savings provision did not apply.
A Patent That Omits an Inventor and Cannot Be Corrected Is Invalid
Turning to the invalidity holding, the Court affirmed that the patents were invalid due to the omission of Huang as a coinventor.
The Court grounded its analysis in the text of § 256(b) itself: “The error of omitting inventors or naming persons who are not inventors shall not invalidate the patent in which such error occurred if it can be corrected”. (Emphasis in the original opinion.) The Court drew the negative implication: a patent is invalid for the error of omitting inventors when that error cannot be corrected.
The court then rejected Fortress’s additional arguments:
(1) The “One True Inventor Is Sufficient” Argument. Fortress argued that as long as one true inventor is named on the patent, the patent is valid. The Court rejected this position as incompatible with the statutory scheme. If omission of an inventor were not an “error” so long as one inventor is named, then § 256’s savings provision would be rendered meaningless, there would be nothing to “save” the patent from. The Court applied the canon against surplusage, citing Sharp v. United States, 580 F.3d 1234, 1238 (Fed. Cir. 2009) (“we must ‘give effect, if possible, to every clause and word of a statute’ and should avoid rendering any of the statutory text meaningless or as mere surplusage”).
(2) The “Whoever” / § 101 Argument. Fortress contended that because 35 U.S.C. § 101 uses the permissive language “[w]hoever invents . . . may obtain a patent thereof,” only one inventor need be listed. The Court disagreed, pointing to 35 U.S.C. § 100(f), which defines “inventor” in the context of joint invention as “the individuals collectively who invented or discovered the subject matter of the invention.” Reading § 101 and § 100(f) together with § 256(b), the Court concluded that when an invention has multiple inventors, they must all be listed. “‘Whoever’ does not mean less than all.”
(3) The Repeal of § 102(f) Argument. Fortress argued that the repeal of 35 U.S.C. § 102(f), which was eliminated by the America Invents Act, supported the proposition that joinder of all inventors is no longer required for validity. The Court rejected this argument, explaining that § 102(f) merely stated that non-inventors are not entitled to a patent, not that all actual inventors need not be named. The Court noted that invalidity for nonjoinder of an inventor was well established even before § 102(f) was enacted, citing Pannu, and that the relevant legislative history indicates that § 102(f) “merely emphasize[d] that it is the inventor that applies for the patent.”
The Court summarized its holding: “[W]e hold that a patent which incorrectly lists its inventor(s) and cannot be corrected according to law is invalid.” Because it was undisputed that Huang was a coinventor, and because Fortress could not correct the inventorship error under § 256, the patents were invalid.
Key Takeaways for Practitioners
1. Inventorship Errors Can Be Fatal—and the Safety Net Has Limits
Fortress Iron makes clear that while § 256 is a savings provision, it is not an unconditional lifeline. If a patent omits a coinventor and the patentee cannot satisfy the notice and hearing requirements of § 256(b), for example, because the omitted coinventor cannot be found, the patent is invalid, full stop. Practitioners should treat inventorship as a threshold issue of patent validity that demands rigorous attention from the earliest stages of the patenting process.
2. Maintain Contact Information for All Contributors
Perhaps the most practical lesson of this case is deceptively simple: maintain current contact information for everyone who contributes to an invention. In Fortress Iron, the critical failure was not a substantive legal error but a logistical one, Huang left his employer in 2016 without leaving forwarding contact information, and neither YD nor Fortress maintained a way to reach him. When inventorship became an issue years later during litigation, this gap proved insurmountable. Companies working with overseas manufacturers, contract research organizations, academic collaborators, or freelance consultants should implement protocols for maintaining current contact information for all individuals who may contribute to inventive subject matter.
3. Conduct Inventorship Analyses Before Filing
This case underscores the importance of conducting a thorough inventorship analysis before filing a patent application, not after litigation has commenced. Fortress’s inventorship problem was not identified until during litigation, when DSI discovered that Lin and Huang had contributed to the invention. Had Fortress conducted a rigorous inventorship determination at the outset, it could have named all four inventors on the original applications and avoided this vulnerability entirely. Practitioners advising clients on patent filings should affirmatively inquire about all individuals who contributed to the conception of any claimed feature, including employees of third-party manufacturers, suppliers, and development partners.
5. “Party Concerned” Under § 256(b) Is Broader Than “Adverse Party”
The court’s rejection of Fortress’s attempt to narrow “party concerned” to those with adversely affected economic interests is significant for future inventorship disputes. Under this holding, any omitted coinventor is a “party concerned” under § 256(b), regardless of whether the correction would benefit or harm that person. This means that a patentee cannot bypass the notice and hearing requirement by arguing that the proposed correction is in the coinventor’s interest.
6. Due Diligence and Portfolio Audits Should Include Inventorship Review
For practitioners involved in patent due diligence, whether in the context of M&A transactions, licensing negotiations, or litigation preparation, Fortress Iron is a reminder that inventorship should be a standard diligence checkpoint. A patent with an unresolvable inventorship defect is not merely at risk; under this holding, it is invalid as a matter of law. Due diligence teams should examine the circumstances under which inventorship was determined, identify any third-party contributors, and assess whether all coinventors have been properly named and can be located if correction becomes necessary.
Conclusion
Fortress Iron, LP v. Digger Specialties, Inc. is a cautionary tale for patent owners and practitioners alike. The Federal Circuit’s decision is grounded in a reading of the statutory text and long-established principles of inventorship law. But its practical consequences are significant: a patent can be rendered permanently invalid by the omission of a coinventor who cannot be located, even when the omission was unintentional and even when all other named inventors are undisputed. The decision reinforces that inventorship is not a ministerial detail to be addressed after the fact, it is a foundational element of patent validity that must be managed with the same care and rigor that practitioners devote to claim drafting, prior art analysis, and compliance with disclosure requirements.
This post was written by Lisa Mueller