MEMORANDUM ***

In this insurance coverage dispute, Max-um Indemnity Company (“Maxum”) appeals the district court’s grant of summary judgment in favor of the three other parties. The court below found that Maxum owed Ames Construction, Inc. (“Ames”) a defense as an additional insured under a policy purchased by Intermountain Industrial, Inc. (“Intermountain”).

We have jurisdiction pursuant to 28 U.S.C. § 1291. ‘We review the district court’s grant of summary judgment de novo.” Pan Pac. Retail Props. Inc. v. Gulf Ins. Co., 471 F.3d 961, 965 (9th Cir. 2006). Montana law applies to this diversity case. See Erie R.R. Co. v. Tompkins, 304 U.S. 64, 78, 58 S.Ct. 817, 82 L.Ed. 1188 (1938). We affirm.

Endorsement # 4 says coverage is provided “only if certificate of insurance has been provided to Company prior to date of loss.” This sentence does not make clear which company must have the certificate in hand for Ames to be covered. That ambiguity must be construed in favor of coverage. See Marie Deonier & Assocs. v. Paul Revere Life Ins. Co., 301 Mont. 347, 9 P.3d 622, 630 (2000).

The “intended use” exclusion did not necessarily apply to the underlying accident. Intermountain supplied both the grating and the clips that were intended to secure it. The uninstalled clips had not yet been put to their intended use, and it is not absolutely clear that the grating had been. Lacking an “unequivocal demonstration” that the claim against Ames did not fall within the policy’s coverage, Max-um had a duty to defend Ames in the underlying law suit. See Farmers Union Mut. Ins. Co. v. Staples, 321 Mont. 99, 90 P.3d 381, 385 (2004).

AFFIRMED.