diff --git a/src/adapters/index.ts b/src/adapters/index.ts
index b4b83e82..2a38dae2 100644
--- a/src/adapters/index.ts
+++ b/src/adapters/index.ts
@@ -1,5 +1,4 @@
 import { readFile, rm } from "node:fs/promises";
-import { createRequire } from "node:module";
 import { sep } from "node:path";
 import { fileURLToPath, pathToFileURL } from "node:url";
 
@@ -19,7 +18,7 @@ import {
 	writeFileRecursive,
 } from "../lib/file";
 import { stringify } from "../lib/json";
-import { findPackageJson, readPackageJson } from "../lib/packageJson";
+import { readPackageJson } from "../lib/packageJson";
 import {
 	addPreview,
 	getPreviews,
@@ -138,18 +137,6 @@ export async function getJsFileExtension(): Promise<string> {
 	return (await checkIsTypeScriptProject()) ? "ts" : "js";
 }
 
-export async function getInstalledMajor(packageName: string): Promise<number> {
-	const require = createRequire(await findPackageJson());
-	try {
-		const { version } = require(`${packageName}/package.json`);
-		const major = Number.parseInt(version.split(".")[0]);
-		return Number.isNaN(major) ? Infinity : major;
-	} catch {
-		// Not installed yet, so assume the newest major.
-		return Infinity;
-	}
-}
-
 export abstract class Adapter {
 	abstract readonly id: string;
 	abstract readonly environmentEnvVarName: string;
diff --git a/src/adapters/nextjs.ts b/src/adapters/nextjs.ts
index 42707749..ca154a33 100644
--- a/src/adapters/nextjs.ts
+++ b/src/adapters/nextjs.ts
@@ -7,13 +7,12 @@ import { pascalCase } from "change-case";
 import {
 	Adapter,
 	checkSourceContains,
-	getInstalledMajor,
 	getJsFileExtension,
 	type PageFile,
 	writeFileIfMissing,
 } from ".";
 import { exists, writeFileRecursive } from "../lib/file";
-import { addDependencies, getNpmPackageVersion } from "../lib/packageJson";
+import { addDependencies, getInstalledMajor, getNpmPackageVersion } from "../lib/packageJson";
 import { dedent, formatObjectKey } from "../lib/string";
 import { checkIsTypeScriptProject, findProjectRoot } from "../project";
 import {
@@ -48,6 +47,7 @@ export class NextJsAdapter extends Adapter {
 		const extension = await getJsFileExtension();
 		const typescript = await checkIsTypeScriptProject();
 		const appRouter = await checkUsesAppRouter();
+		const supportsCacheLife = (await getInstalledMajor("next")) >= 16;
 
 		await writeFileIfMissing(
 			new URL(`prismicio.${extension}`, sourceRoot),
@@ -81,7 +81,7 @@ export class NextJsAdapter extends Adapter {
 		if (appRouter) {
 			await writeFileIfMissing(
 				new URL(`app/api/revalidate/route.${extension}`, sourceRoot),
-				revalidateRouteTemplate({ supportsCacheLife: (await getInstalledMajor("next")) >= 16 }),
+				revalidateRouteTemplate({ supportsCacheLife }),
 			);
 		}
 	}
diff --git a/src/lib/packageJson.ts b/src/lib/packageJson.ts
index 5afddd5a..4aaf16e5 100644
--- a/src/lib/packageJson.ts
+++ b/src/lib/packageJson.ts
@@ -1,4 +1,5 @@
 import { readFile, writeFile } from "node:fs/promises";
+import { createRequire } from "node:module";
 import { fileURLToPath } from "node:url";
 
 import detectIndent from "detect-indent";
@@ -59,6 +60,20 @@ export async function addDependencies(dependencies: Record<string, string>): Pro
 	});
 }
 
+export async function getInstalledMajor(packageName: string): Promise<number> {
+	const require = createRequire(await findPackageJson());
+	try {
+		const { version } = require(`${packageName}/package.json`);
+		const major = Number.parseInt(version.split(".")[0]);
+		return Number.isNaN(major) ? Infinity : major;
+	} catch {
+		const { dependencies, devDependencies, peerDependencies } = await readPackageJson();
+		const range = { ...peerDependencies, ...dependencies, ...devDependencies }[packageName] ?? "";
+		const major = /^[\^~]?(\d+)/.exec(range)?.[1];
+		return major ? Number(major) : Infinity;
+	}
+}
+
 // Returns the packages whose major version changed between two reads of package.json.
 export function getMajorDependencyUpdates(
 	before: PackageJson,
diff --git a/test/gen-setup.test.ts b/test/gen-setup.test.ts
index 2594b30c..6962757f 100644
--- a/test/gen-setup.test.ts
+++ b/test/gen-setup.test.ts
@@ -289,6 +289,25 @@ it("works when Next.js is declared but not installed", async ({ expect, project,
 	await expect(project).toHaveFile("app/api/revalidate/route.js");
 });
 
+it("generates a Next.js 15 revalidate route before Next.js is installed", async ({
+	expect,
+	project,
+	prismic,
+}) => {
+	await rm(new URL("node_modules/next/", project), { recursive: true });
+	await writeFile(
+		new URL("package.json", project),
+		JSON.stringify({ dependencies: { next: "^15.0.0" } }),
+	);
+
+	const { stderr, exitCode } = await prismic("gen", ["setup", "--no-install"]);
+	expect(exitCode, stderr).toBe(0);
+
+	await expect(project).toHaveFile("app/api/revalidate/route.js", {
+		contains: 'revalidateTag("prismic");',
+	});
+});
+
 it(
 	"prints SvelteKit instructions when the project already has a root layout",
 	{ timeout: 30_000 },