In re Tanaka: Adding a Narrower Dependent Claim Is a Reissuable Error

A reissue application must rest on an “error” that makes the patent wholly or partly inoperative or invalid. For years it was debated whether a patent owner who was satisfied with every original claim could still file a reissue to add narrower claims. In re Tanaka (Fed. Cir. 2011) answered that question: yes, it can.

The decision is short, but it shapes how patent owners think about reissue today. It turned a once-uncertain practice into an accepted way to build fallback positions into an issued patent.

The question in Tanaka

The patent owner filed a reissue application that kept all of the original claims and added one new dependent claim, narrower than a claim already in the patent. The reissue declaration identified the error as the failure to include that narrower claim.

The Office’s appeals board rejected the reissue. Its reasoning was that the original patent was not defective: the owner kept every original claim, so nothing in the patent was inoperative or invalid. Adding a narrower claim, in the board’s view, was not correcting an error at all.

What the Federal Circuit held

The Federal Circuit reversed. It held that the omission of a narrower dependent claim is the kind of error that § 251 allows a patent owner to correct, even when the owner keeps every original claim.

The court relied on a long line of authority recognizing that reissue may be used to add narrower claims as a hedge against the possible invalidity of broader ones. It treated that practice as well settled and declined to read § 251 as requiring that an original claim be defective before reissue is available.

The holding is narrow in one respect: it addresses whether the error requirement is met. The new claim must still satisfy every other requirement of patentability, and the reissue as a whole is still examined under the usual standards.

Why hedge claims matter

Broad claims are the most valuable claims in a patent, and the most exposed. If an accused infringer later finds prior art that anticipates or renders a broad claim obvious, a patent with no narrower claims may be left with nothing.

Dependent claims add limitations that can distinguish the invention from prior art that defeats the broad claim. They also give a court or the Patent Trial and Appeal Board more options in claim construction and validity disputes. A patent owner who realizes after grant that a commercially important embodiment is not separately claimed can use reissue to add it.

Tanaka confirms that the owner does not have to give up or narrow the broad claims to do this. The original claims stay in the patent, and the narrower claims sit alongside them.

Practice since Tanaka

USPTO examining guidance in MPEP Chapter 1400 reflects Tanaka: adding a narrower dependent claim while retaining the original claims can be the error identified in the reissue declaration under 37 C.F.R. § 1.175. The declaration still has to identify that error specifically, for example by naming the claim that lacked a narrower dependent.

Patent owners weighing this approach usually consider several practical points:

• The whole patent is reopened. Even if the owner only wants to add claims, the examiner can reject original claims on any applicable ground. The reissue may end with narrower original claims. See reissue procedure, advantages and pitfalls.
• Intervening rights. New claims in a reissue can trigger intervening rights under 35 U.S.C. § 252 for third parties who began their activity before the reissue. Original claims carried through unchanged generally are not affected.
• Recapture. Narrower claims rarely raise recapture issues, but any claim broader than an original claim in some respect must be checked under the rule discussed in the In re Youman article.
• Alternatives. If a continuation application is still pending, adding claims there is often simpler. Ex parte reexamination also allows new claims, but only in response to a substantial new question of patentability and only if they do not enlarge scope.

Where Tanaka fits

Situation	Is there a reissuable error?
Original claims too broad and invalid over prior art	Yes
Original claims too narrow (within two years of grant)	Yes, broadening reissue
Original claims fine, but a narrower dependent claim was omitted	Yes, after Tanaka
Purely clerical mistake	Usually handled by certificate of correction instead

For background on the reissue statute itself, see the reissue applications guide.

Key takeaways

• In re Tanaka (Fed. Cir. 2011) held that omitting a narrower dependent claim is an error that can support reissue.
• The owner may keep every original claim unchanged and add hedge claims.
• The reissue declaration must still identify the error specifically.
• Reissue reopens the whole patent, so the benefits of added claims must be weighed against examination risk and intervening rights.