facts, we do not recount them here. We affirm.

1. The district court properly determined that the Durbins cannot require

Mountain West to “stack” liability coverage limits under the policy at issue in this

case. The terms of Mountain West’s policy clearly state that “the most [Mountain

West] will pay” as a result of “any one ‘accident’ is the Limit of Insurance for

Liability Coverage shown in the Declarations.” That limit is $500,000, the same

amount that Mountain West has already paid to the Durbins. If those terms are

enforceable, then the policy clearly prohibits stacking. To the extent that the

Durbins may have expected otherwise, that expectation was unreasonable. See

Fisher v. State Farm Mut. Auto. Ins. Co., 305 P.3d 861, 867 (Mont. 2013) (holding

that the reasonable expectations doctrine does not apply when a policy’s terms

“clearly demonstrate an intent to exclude coverage”).

2 These terms do not violate public policy and are therefore enforceable under

Montana law. An insurance policy that provides illusory coverage—in other

words, that “contains provisions that defeat coverage for which the insurer has

received valuable consideration”—is against public policy, and the offending

provisions are unenforceable. Hardy v. Progressive Specialty Ins. Co., 67 P.3d

892, 899–900 (Mont. 2003). If a single insurance policy provides a person with

multiple sets of first-party coverage that is “personal and portable,” then the person

must be allowed to “stack” the limits of that coverage and receive a higher

maximum payout. See Cross v. Warren, 435 P.3d 1202, 1208 (Mont. 2019)

(collecting cases). However, coverage is “personal and portable” only if it protects

the insured person in “all circumstances.” Jacobson v. Implement Dealers Mut.

Ins. Co., 640 P.2d 908, 912 (Mont. 1982). Third-party liability coverage is not

portable under Montana law because such coverage “is not . . . portable and

applicable in ‘all circumstances.’” Cross, 435 P.3d at 1208. Instead, such

coverage applies only when the insured is operating a vehicle covered by that

insurance. Id. Because the coverage applies only under specific circumstances,

refusing to stack limits does not defeat coverage for which the insurer has received

consideration. Id. at 1209–10.

That the Durbins received a full assignment of rights under the Mountain

West policy is irrelevant. An assignment of rights does not make the liability

3 coverage “personal and portable” because the coverage still applies “only with

respect to an accident arising out of the ownership, maintenance, or use of an auto

or trailer.” Id. at 1208; see also id. at 1212 n.1 (McKinnon, J., concurring)

(recognizing that liability coverage “does not become personal or portable through

an assignment”). Even if the Durbins became insureds through the assignment of

rights, their status as insureds does not allow them to stack liability coverage

limits.

2 The decision whether to certify an issue to a state court of last resort

“rests in the sound discretion of the federal court.” Lehman Bros. v. Schein, 416

U.S. 386, 391 (1974). Even if state law is unclear, “resort to the certification

process is not obligatory.” Riordan v. State Farm Mut. Auto. Ins. Co., 589 F.3d

999, 1009 (9th Cir. 2009). Given the ample precedent describing when insurance

coverage is “personal and portable” for purposes of stacking coverage limits, the

district court did not abuse its discretion when it determined that it could apply

existing law to the Durbins’ claims. 1

AFFIRMED.

1 For similar reasons, the Durbins’ Motion for Certification to the Montana State Supreme Court, Dkt. 5, is denied.

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