“Winning” Prosecution Arguments Can Invalidate Your Patent As Indefinite

Sheppard Mullin Richter & Hampton LLP

Sheppard Mullin Richter & Hampton LLP

On February 10, 2021, the Federal Circuit in Infinity Computer Products, Inc. v. Oki Data Americas, Inc., No. 20-1189 (Fed. Cir. 2021) affirmed a decision by the U.S. District Court of Delaware that patent claims were invalid for indefiniteness based on conflicting positions taken by the patentee during prosecution. Specifically, the Federal Circuit held that the conflicting positions leave one of ordinary skill without reasonable certainty regarding the scope of the invention. This Federal Circuit decision is a reminder to patent applicants that piecemeal success before the Patent Office that does not conform to a coherent overarching prosecution strategy can invalidate patent rights.


In Infinity Computer Products, the claims at issue were part of a continuation-in-part application directed to using a facsimile machine as a printer or scanner for a computer. To overcome prior art during prosecution of the application, the patentee successfully argued that a facsimile machine and a computer were connected with a claimed “passive link” that ends at an I/O bus inside the computer. After further prosecution, a patent was granted. Later, the patent was subjected to ex parte reexaminations. In one reexamination, the patentee sought to antedate prior art by claiming priority to a parent case. In establishing claim support in the parent case, the patentee successfully but inconsistently argued that the claimed “passive link” ends at a port of a computer. The district court found the patentee’s positions regarding endpoints of the “passive link” in the original prosecution and the later reexamination to be conflicting, thus rendering the extent of the claimed “passive link” not reasonably certain. The district court accordingly concluded that the claims were invalid for indefiniteness.

Federal Circuit Decision

As indefiniteness is ultimately a question of law, the Federal Circuit reviewed the case de novo. Relying on its precedent, the Federal Circuit stated that “[i]ndefiniteness may result from inconsistent prosecution history statements where the claim language and specification on their own leave an uncertainty that, if unresolved, would produce indefiniteness.” Infinity Computer Products, 20-1189 at 12. The Federal Circuit noted that the public-notice function of a patent and its prosecution history requires holding patentees to their own declarations. Based on the facts before it, the Federal Circuit determined that holding the patentee to its inconsistent positions resulted in a plain contradiction that precluded notice to the public about what remained in the public domain. Thus, the Federal Circuit found no legal error and affirmed the district court’s decision.


Proceedings before the Patent Office are often complex and enduring. Many positions can be advanced by a patentee against myriad Patent Office rejections in different stages over long periods of time. Infinity Computer Products is the latest Federal Circuit decision to remind patentees that, no matter how involved or extensive the prosecution effort, positions taken in prosecution should remain consistent over the long term. Even if they individually achieve a favorable outcome on a particular issue, prosecution positions that conflict with each other will ultimately jeopardize patent rights. Accordingly, patent applicants should proceed at each stage of prosecution with all stages in mind. Failure to do so can open the door to patent invalidation.

DISCLAIMER: Because of the generality of this update, the information provided herein may not be applicable in all situations and should not be acted upon without specific legal advice based on particular situations.

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