The shield covers a divisional, and only if you filed it

How to read the ledger below. Each numbered point carries the kind of evidence behind it. ESTABLISHED is stated in the authority's own text, with a locator. IMPLEMENTED is the rule as the authority actually applied it. OBSERVED is carried by a source outside this one. ASSUMED is the drafter's inference, flagged as such and not the authority speaking. Quotations are checked against a cached copy of the primary source by script.

In one paragraph

The third sentence of 35 U.S.C. 121 establishes a safe harbor, and MPEP 804.01 sets out how the Office applies it. A patent issuing from an application in which the Office required restriction, or from an application filed as a result of that requirement, cannot be used as a double patenting reference against a divisional or against the original application, provided the divisional was filed before that patent issued. Four conditions all have to hold. The Office must have made the requirement rather than the applicant splitting voluntarily, the claims must have been formally entered and restricted in and removed from the earlier application, the branch must be a divisional because the Federal Circuit has limited the protection to divisionals rather than all continuing applications, and consonance with the examiner line of demarcation must be maintained in what the divisional claims. Eight named situations put a filing outside the shield, a continuation in part is one of them, and a patentee cannot amend or redesignate its way back in afterwards.

Reader summary

The third sentence of section 121 does something unusual: it makes a patent unusable as a reference. Where the Office required restriction, the patent issuing from one branch cannot be used against a divisional of the other, in the Office or in court, provided the divisional was filed before that patent issued.

The conditions are narrow and each of them fails in practice for a different reason.

The Office must have made the requirement. A voluntary split gets nothing, and the Office's guidance is specific about what "as a result of" means: the claims must have been formally entered, restricted in, and removed from the earlier application before being filed in the divisional.

The filing must be a divisional. The Federal Circuit has said the protection is limited to divisional applications, which excludes continuations and continuations-in-part. A continuation-in-part carrying restricted claims is called out as its own exception.

Consonance must be maintained. The line of demarcation the examiner drew between the independent and distinct inventions has to survive into the divisional's claims. Claims changed in material respects, or added beyond the restricted scope, cross that line and the prohibition stops applying.

And it cannot be recovered later. Two decisions the Office cites hold that a patentee cannot amend its way into the safe harbor after the fact by cutting a continuation-in-part back to the parent's subject matter and redesignating it a divisional.

Why this matters when you are drafting

Label the branch correctly and file it as a divisional. Claim 4. The distinction between a divisional and a continuation is decisive here in a way it is not for most purposes, and the Federal Circuit has said so.

The record has to show the Office required it. Claims 3 and 5. Voluntary splits get nothing, and the enter-restrict-remove sequence in the parent is what proves the branch was filed as a result of the requirement.

Consonance is a drafting constraint on the divisional's claims, not a filing formality. Claims 6, 7 and 8. The examiner's line of demarcation has to survive into what you claim. Broadening a divisional's claims past the restricted group is the ordinary way this protection is lost, and it happens during prosecution, long after filing.

Timing: the divisional must be filed before the other patent issues. Claim 1. That is in the statute, and it is a hard date tied to issuance of the sibling rather than to anything in the divisional's own prosecution.

A continuation-in-part is outside the shield and cannot be brought inside later. Claims 9 and 10. Two decisions foreclose the amend-and-redesignate route. Where added matter is necessary, the safe harbor is not available for that branch.

Losing consonance is not the same as losing the case. Claim 14. The claims may still be patentably distinct, and a terminal disclaimer remains available. Read this with terminal-disclaimer-mechanics, which carries what a disclaimer costs, and with in-re-cellect and allergan-v-msn, which carry what double patenting does to term.

What the authority establishes

[ESTABLISHED, the statute itself, and this is the operative sentence] "A patent issuing on an application with respect to which a requirement for restriction under this section has been made, or on an application filed as a result of such a requirement, shall not be used as a reference either in the Patent and Trademark Office or in the courts against a divisional application or against the original application or any patent issued on either of them, if the divisional application is filed before the issuance of the patent on the other application." (35 U.S.C. 121, as reproduced in MPEP 804.)

[ESTABLISHED, the same sentence in the Office's own summary] "The third sentence of 35 U.S.C. 121 prohibits the use of a patent issuing on an application in which a requirement for restriction has been made, or on an application filed as a result of such a requirement, as a reference against any divisional application in a nonstatutory double patenting rejection, if the divisional application is filed before the issuance of the patent." (MPEP 804.01.)

[ESTABLISHED, the first and most important condition] "The 35 U.S.C. 121 prohibition applies only where the Office has made a requirement for restriction. The prohibition does not apply where the divisional application was voluntarily filed by the applicant and not in response to an Office requirement for restriction." (MPEP 804.01.)

[ESTABLISHED, the second condition, and it excludes most continuing applications] The Federal Circuit "has concluded that the protection of 35 U.S.C. 121 does not extend to all types of continuing applications, stating that" (MPEP 804.01.) "the protection afforded by section 121 to applications (or patents issued therefrom) filed as a result of a restriction requirement is limited to divisional applications." (Pfizer v. Teva, quoted at MPEP 804.01.) A continuation is not a divisional for this purpose.

[ESTABLISHED, what "as a result of" requires mechanically] "In order to obtain the benefit of 35 U.S.C. 121, claims must be formally entered, restricted in, and removed from an earlier application before they are filed in a divisional application" (MPEP 804.01, exception A.) Three steps, all in the parent, all before the divisional exists.

[ESTABLISHED, the third condition, consonance] "Section 121 shields claims against a double patenting challenge if consonance exists between the divided groups of claims and an earlier restriction requirement." (Geneva Pharmaceuticals, quoted at MPEP 804.01 and 804.04.)

[ESTABLISHED, what consonance means] "Consonance requires that the line of demarcation between the" independent and distinct inventions "that prompted the restriction requirement be maintained" (Symbol Technologies, quoted at MPEP 804.01 and 804.04.), and where that line is crossed the prohibition of the third sentence does not apply.

[ESTABLISHED, how consonance is lost in practice] The protection fails where the claims "are not consonant with the restriction requirement made by the examiner, since the claims have been changed in material respects from the claims at the time the requirement was made. For example, the divisional application filed includes additional claims not consonant in scope with the original claims subject to restriction in the parent." (MPEP 804.01, exception B.)

[ESTABLISHED, and this is the exception a continuation practitioner will meet] The prohibition does not apply where "The second application is a continuation-in-part (CIP) application that includes claims restricted from the original application." (MPEP 804.01, exception H.)

[ESTABLISHED, the safe harbor cannot be entered retroactively] "a patentee cannot retroactively recover the safe harbor protection of 35 U.S.C. 121 against nonstatutory double patenting by amending a patent that issued from a continuation-in-part application to only subject matter in the parent application and redesignating the CIP as a divisional of the parent application." *(MPEP 804.01, citing In re Janssen Biotech and G.D. Searle.)* The Office quotes Janssen for the proposition that a "patent owner cannot retroactively bring its challenged patent within the scope of the safe-harbor provision by amendment in a reexamination proceeding." (MPEP 804.01.)

[ESTABLISHED, the six other exceptions, listed so none is a surprise] The prohibition also does not apply where the restriction requirement was withdrawn because it was made subject to the nonallowance of generic or linking claims that were later allowed (exception C); where the requirement was made only by an International Searching or Preliminary Examining Authority in an international application, though it DOES apply to a lack-of-unity holding made in a national stage application under 35 U.S.C. 371 (exception D); where the requirement was withdrawn by the examiner before the patent issued (exception E); where the claims are to the "same invention" so that a statutory rejection under 35 U.S.C. 101 applies instead (exception F); and where a product-and-process restriction was made subject to nonallowance of the product and process claims are later rejoined (exception G). (MPEP 804.01.)

[ESTABLISHED, the shield does not reach identical claims] "35 U.S.C. 121 does not prevent a double patenting rejection when the identical invention is claimed in the divisional application and the application/patent in which a restriction requirement was made." (MPEP 804.01.)

[ESTABLISHED, what the safe harbor covers, which is broader than it first looks] The prohibition "applies to requirements for restriction between independent or distinct inventions" of the kinds the manual treats elsewhere, "so long as the claims in each application are filed as a result of such requirement." (MPEP 804.01.)

[ESTABLISHED, what happens when consonance is lost, which is not automatic invalidity] "However, even if such consonance is lost, double patenting does not follow if the requirements of Section 121 are met or if the claims are in fact patentably distinct" (Applied Materials, quoted at MPEP 804.04.), and "The purpose of Section 121 is to accommodate administrative convenience and to protect the patentee from technical flaws based on this unappealable examination practice." (Applied Materials, quoted at MPEP 804.04.)

[ESTABLISHED, why the Office treats restriction requirements carefully] The provision "imposes a heavy burden on the Office to guard against erroneous requirements for restrictions" (MPEP 804.01.), which is the Office's own statement of what the shield costs it.

[IMPLEMENTED, the practical shape of the test] Claims 3, 4, 5, 6 and 9 are four independent gates and every one of them must hold: an Office requirement, a divisional rather than any other continuing type, the formal enter-restrict-remove sequence, and consonance maintained. Failing any one puts the branch outside the shield entirely, and claim 10 means the failure cannot be repaired afterwards.

[ASSUMED, drafter's inference, flagged as such] The safe harbor is the one route by which a family can hold multiple patents on related inventions without terminal disclaimers, and claim 4 means that route runs only through divisionals. A practice that files continuations by default rather than divisionals where a restriction was made is giving up the shield for nothing. The manual does not frame it as a choice; this follows from claims 3 and 4 read against the terminal-disclaimer machinery in terminal-disclaimer-mechanics.

Quotations, verified against the source

All from MPEP 804, 804.01 and 804.04 as cached, including the statutory text and the case law those sections quote. Locators are section numbers; an MPEP page carries no pagination a page-mapper can anchor.

"A patent issuing on an application with respect to which a requirement for restriction under this section has been made, or on an application filed as a result of such a requirement, shall not be used as a reference either in the Patent and Trademark Office or in the courts against a divisional application or against the original application or any patent issued on either of them, if the divisional application is filed before the issuance of the patent on the other application." (35 U.S.C. 121, MPEP 804.)
"The third sentence of 35 U.S.C. 121 prohibits the use of a patent issuing on an application in which a requirement for restriction has been made, or on an application filed as a result of such a requirement, as a reference against any divisional application in a nonstatutory double patenting rejection, if the divisional application is filed before the issuance of the patent." (MPEP 804.01.)
"The 35 U.S.C. 121 prohibition applies only where the Office has made a requirement for restriction. The prohibition does not apply where the divisional application was voluntarily filed by the applicant and not in response to an Office requirement for restriction." (MPEP 804.01.)
"has concluded that the protection of 35 U.S.C. 121 does not extend to all types of continuing applications, stating that" (MPEP 804.01.)
"the protection afforded by section 121 to applications (or patents issued therefrom) filed as a result of a restriction requirement is limited to divisional applications." (MPEP 804.01.)
"In order to obtain the benefit of 35 U.S.C. 121, claims must be formally entered, restricted in, and removed from an earlier application before they are filed in a divisional application" (MPEP 804.01.)
"Section 121 shields claims against a double patenting challenge if consonance exists between the divided groups of claims and an earlier restriction requirement." (MPEP 804.01.)
"Consonance requires that the line of demarcation between the" (MPEP 804.01.)
"that prompted the restriction requirement be maintained" (MPEP 804.01.)
"are not consonant with the restriction requirement made by the examiner, since the claims have been changed in material respects from the claims at the time the requirement was made. For example, the divisional application filed includes additional claims not consonant in scope with the original claims subject to restriction in the parent." (MPEP 804.01.)
"The second application is a continuation-in-part (CIP) application that includes claims restricted from the original application." (MPEP 804.01.)
"a patentee cannot retroactively recover the safe harbor protection of 35 U.S.C. 121 against nonstatutory double patenting by amending a patent that issued from a continuation-in-part application to only subject matter in the parent application and redesignating the CIP as a divisional of the parent application." (MPEP 804.01.)
"patent owner cannot retroactively bring its challenged patent within the scope of the safe-harbor provision by amendment in a reexamination proceeding." (MPEP 804.01.)
"35 U.S.C. 121 does not prevent a double patenting rejection when the identical invention is claimed in the divisional application and the application/patent in which a restriction requirement was made." (MPEP 804.01.)
"applies to requirements for restriction between independent or distinct inventions" (MPEP 804.01.)
"so long as the claims in each application are filed as a result of such requirement." (MPEP 804.01.)
"imposes a heavy burden on the Office to guard against erroneous requirements for restrictions" (MPEP 804.01.)
"However, even if such consonance is lost, double patenting does not follow if the requirements of Section 121 are met or if the claims are in fact patentably distinct" (MPEP 804.04.)
"The purpose of Section 121 is to accommodate administrative convenience and to protect the patentee from technical flaws based on this unappealable examination practice." (MPEP 804.04.)
"does apply to requirements for restriction (lack of unity of invention holdings) made in national stage applications submitted under 35 U.S.C. 371." (MPEP 804.01.)

Tensions and open questions

This record is guidance about law, not law. The statutory sentence in claim 1 binds. Claims 2 through 15 are the Office's account of how it and the courts apply that sentence, and the decisions behind the exceptions have not been read here. Where a practitioner needs the holding rather than the summary, the citations are the starting point.

The MPEP revision is [R-07.2022] and this cache was taken 2026-08-14. Guidance moves. Nothing in the exceptions list is dated in a way that shows whether later case law has shifted it, and the manual's own revision marker is four years old relative to this cache.

Whether the shield survives a divisional-of-a-divisional is not addressed by what was read. Claim 4 limits the protection to divisionals; the passages read do not say how a chain of divisionals is treated.

Exception E, withdrawal of the requirement, is stated without a limit in time. The manual says withdrawal before the patent issues removes the protection and describes the requirement as disappearing. What that means for a divisional already filed in reliance on it is not spelled out in what was read.

Consonance's boundary is stated only by example. Claim 8 gives one, additional claims not consonant in scope. How far a divisional's claims may be amended during prosecution before the line is crossed is a fact question the manual does not resolve.

What this record does and does not cover

MPEP 804.01 was read end to end, along with the statutory reproductions in MPEP 804 and the consonance passage in MPEP 804.04.

What was NOT read, and is therefore outside what this record can support: the rest of MPEP 804, which is long and mostly about the double-patenting doctrine rather than the safe harbor, and every decision the exceptions cite. Pfizer v. Teva, Geneva Pharmaceuticals, Symbol Technologies, Gerber Garment, Applied Materials, In re Janssen Biotech and G.D. Searle are known here only through the manual's quotation of them and have no record in this corpus. This record says nothing about restriction practice itself, meaning when a restriction requirement is proper, which is a separate body of guidance.

Currency

This record was verified against its primary source on 2026-08-15. That is a fidelity check: the quotations, locators and attribution are accurate to that source. Whether the authority has since been narrowed, distinguished, abrogated or reversed has not been checked here. Confirm it still stands before relying on it.

The shield only covers a divisional, and only if you filed it