Get inventorship wrong, and a valuable patent can become unenforceable. A patent must accurately name the individuals who invented the claimed subject matter. If one or more inventors are omitted, a court may hold the patent invalid—and, in some circumstances, the defect may be uncorrectable. In Fortress Iron, LP v. Digger Specialties, Inc., No. 2024-2313 (Fed. Cir. April 2, 2026), the Federal Circuit affirmed summary judgment invalidating two patents because a co-inventor was omitted and could not be added under the law that allows correction of inventorship (35 U.S.C. § 256). For companies, inventorship is best managed through a defined, repeatable process from early development through issuance, rather than addressed only at filing.
This risk is most acute in collaborative development environments—particularly where overseas manufacturers, key suppliers, consultants, or third-party engineers propose or implement technical solutions. Where external parties contribute to the conception of subject matter that ultimately appears in the claims, inventorship may extend beyond the company’s employees. Companies should therefore (1) identify potential inventors early, (2) document contributions contemporaneously, and (3) ensure that all contributors are subject to appropriate agreements and remain reachable well before a patent is allowed.
In Fortress Iron, the patents covered pre-assembled vertical cable railing panels. Fortress began with an internal concept, but development proceeded in coordination with foreign manufacturing and quality-control partners: Yinxin Handicrafts Co., Ltd. and Quan Zhou Yoddex Building Material Co., Ltd. Two employees of Quan Zhou Yoddex proposed specific technical changes that addressed cable rotation during tensioning. Those changes were incorporated into the final design and the asserted claims; however, neither contributor was named as an inventor when the patents issued. The case reflects a common scenario for companies that rely on supplier input to address engineering challenges during product development.
The inventorship issue arose during infringement litigation. Fortress was able to locate and add one contributor, but the other had left his employer and could not be located. Fortress sought correction under Section 256 (for issued patents), contending that adding the omitted individual would not be prejudicial because he had assigned his rights.
The courts rejected that position. The Federal Circuit emphasized that Section 256 requires notice to all “parties concerned,” irrespective of patent ownership or whether correction appears non-prejudicial. Because the omitted co-inventor could not be located—and therefore could not receive notice—the statute could not be used to correct the defect. Stated differently, an inability to locate an omitted inventor after a patent grants may foreclose a statutory correction and expose the patent to invalidity. The case illustrates an enforcement risk: once litigation is underway, correction options may be constrained, and difficulties locating former third-party contributors can become a validity issue.
The Federal Circuit also rejected arguments that the America Invents Act materially reduced the consequences of incorrect inventorship. Because inventorship remains a statutory requirement, and an uncorrectable error may continue to threaten a patent’s validity. Accordingly, implementing disciplined inventorship practices during development and prosecution is typically far less costly, provide more flexible options, and create less risk than attempting to address inventorship defects during patent enforcement.
Several practical takeaways follow:
First, inventorship is not limited to employees; partners, contractors, suppliers, and other collaborators may qualify as inventors if they contribute to the conception of subject matter reflected in at least one claim.
Second, because inventorship turns on claim scope and technical contribution—not job title or project role—contemporaneous documentation is essential.
Third, assignment instruments address ownership, but they do not, standing alone, fix inventorship defects.
Fourth, where a patent must be corrected in anticipation of enforcement and an omitted inventor cannot be located despite good-faith efforts, a reissue application may provide a path to correction, including use of a substitute statement in lieu of an inventor’s oath or declaration.
In addition, in certain circumstances, the assignee of the entire interest may sign the oath or declaration (e.g., where the reissue does not enlarge claim scope, or where the original application was filed by the assignee under 37 C.F.R. § 1.46).
Finally, inventorship disputes often surface only after a patent is asserted, when correction options may be narrower and the practical challenges of locating third-party contributors are greatest.
Inventorship checklist (invention disclosure form and patent applications)
- At project kickoff/early development
- Establish an inventorship intake and checkpoint routine.
- Maintain dated records linking individuals to claim-relevant ideas.
- Train teams to distinguish between inventors and contributors and that non-employees may be inventors.
- Require written disclosure of changes/improvements/solutions proposed by partners and the specific individuals who developed them.
- Use agreements addressing assignment from inventors to the parties, ownership as between the parties, cooperation to execute documents, and current contact information.
- At prosecution milestones/Before paying the issue fee
- Before paying the issue fee, confirm inventorship against the allowed claims.
- Confirm you can reach each inventor (including third parties).
- Maintain last known addresses of inventors, especially if such inventor is not an employee of or no longer an employee of the company in the event needed at later stages.
- Do not assume assignments cure inventorship defects.
- When claims change, reassess inventorship and address it before issuance.
Inventorship is a validity issue that can materially impair patent value. Companies—particularly those developing products with third parties—should implement an early, documented inventorship process and conduct a final review before issuance. Fortress Iron serves as a reminder that when inventorship errors cannot be corrected, the consequences can include the complete loss of patent protection.
