diff --git a/.changeset/vitest-plugin-require-condition.md b/.changeset/vitest-plugin-require-condition.md
new file mode 100644
index 00000000000..d5f5c0ba3d7
--- /dev/null
+++ b/.changeset/vitest-plugin-require-condition.md
@@ -0,0 +1,5 @@
+---
+"@cloudflare/vitest-plugin": patch
+---
+
+Fix Worker tests failing when CommonJS dependencies require packages with separate `import` and `require` entries on Vite 8. The fix needs Vite 8.2.1 or later; Vite 8.0.x, 8.1.x and 8.2.0 stay affected.
diff --git a/packages/vitest-plugin/src/pool/module-fallback.ts b/packages/vitest-plugin/src/pool/module-fallback.ts
index 641a286d9f4..e39875f7fda 100644
--- a/packages/vitest-plugin/src/pool/module-fallback.ts
+++ b/packages/vitest-plugin/src/pool/module-fallback.ts
@@ -328,11 +328,17 @@ async function viteResolve(
 	referrer: string,
 	isRequire: boolean
 ): Promise<string> {
-	const resolved = await vite.pluginContainer.resolveId(specifier, referrer, {
-		ssr: true,
-		// https://github.com/vitejs/vite/blob/v5.1.4/packages/vite/src/node/plugins/resolve.ts#L178-L179
-		custom: { "node-resolve": { isRequire } },
-	});
+	const resolved = await vite.environments.ssr.pluginContainer.resolveId(
+		specifier,
+		referrer,
+		{
+			// Vite 8.2.1, and later, picks the `require` or `import` export condition from `kind`
+			kind: isRequire ? "require-call" : "import-statement",
+			// Vite 7 and earlier read `isRequire` from here instead
+			// https://github.com/vitejs/vite/blob/v5.1.4/packages/vite/src/node/plugins/resolve.ts#L178-L179
+			custom: { "node-resolve": { isRequire } },
+		}
+	);
 	if (resolved === null) {
 		// Vite's resolution algorithm doesn't apply Node resolution to specifiers
 		// starting with a dot. Unfortunately, the `@prisma/client` package includes
diff --git a/packages/vitest-plugin/test/cjs-require.test.ts b/packages/vitest-plugin/test/cjs-require.test.ts
index 6a9d50748a7..58593ca550b 100644
--- a/packages/vitest-plugin/test/cjs-require.test.ts
+++ b/packages/vitest-plugin/test/cjs-require.test.ts
@@ -32,3 +32,48 @@ test(
 		expect(await result.exitCode).toBe(0);
 	}
 );
+
+test(
+	"resolves requires from CJS modules to the require export condition",
+	{ timeout: 45_000 },
+	async ({ expect, seed, vitestRun }) => {
+		await seed({
+			"vitest.config.mts": vitestConfig(),
+			"node_modules/cjs-demo/package.json": JSON.stringify({
+				name: "cjs-demo",
+				version: "1.0.0",
+				main: "index.cjs",
+			}),
+			"node_modules/cjs-demo/index.cjs": dedent`
+				module.exports = require("dual-demo");
+			`,
+			"node_modules/dual-demo/package.json": JSON.stringify({
+				name: "dual-demo",
+				version: "1.0.0",
+				exports: {
+					".": {
+						import: "./index.mjs",
+						require: "./index.cjs",
+					},
+				},
+			}),
+			"node_modules/dual-demo/index.mjs": dedent`
+				export const format = "esm";
+			`,
+			"node_modules/dual-demo/index.cjs": dedent`
+				module.exports = { format: "cjs" };
+			`,
+			"index.test.ts": dedent`
+				import { expect, it } from "vitest";
+				import demo from "cjs-demo";
+
+				it("loads the CJS entry of a dual-format package", () => {
+					expect(demo.format).toBe("cjs");
+				});
+			`,
+		});
+
+		const result = await vitestRun();
+		expect(await result.exitCode).toBe(0);
+	}
+);
diff --git a/packages/vitest-plugin/test/module-fallback.test.ts b/packages/vitest-plugin/test/module-fallback.test.ts
index 5e87ceb4837..29ef789a5ce 100644
--- a/packages/vitest-plugin/test/module-fallback.test.ts
+++ b/packages/vitest-plugin/test/module-fallback.test.ts
@@ -17,13 +17,18 @@ import {
 } from "../src/shared/module-path";
 import type { Vite } from "vitest/node";
 
-// The fallback handler only reads `vite.pluginContainer.resolveId`, and only
-// when a specifier can't be resolved directly from the filesystem. Returning
-// `null` mimics Vite failing to resolve, exercising the 404 fall-through.
+// The fallback handler only reads
+// `vite.environments.ssr.pluginContainer.resolveId`, and only when a specifier
+// can't be resolved directly from the filesystem. Returning `null` mimics Vite
+// failing to resolve, exercising the 404 fall-through.
 function fakeVite(): Vite.ViteDevServer {
 	return {
-		pluginContainer: {
-			resolveId: async () => null,
+		environments: {
+			ssr: {
+				pluginContainer: {
+					resolveId: async () => null,
+				},
+			},
 		},
 	} as unknown as Vite.ViteDevServer;
 }
@@ -37,8 +42,12 @@ function fakeVite(): Vite.ViteDevServer {
 // same rooted path that branch would have produced reaches the same place.
 function fakeViteResolvingTo(id: string): Vite.ViteDevServer {
 	return {
-		pluginContainer: {
-			resolveId: async () => ({ id }),
+		environments: {
+			ssr: {
+				pluginContainer: {
+					resolveId: async () => ({ id }),
+				},
+			},
 		},
 	} as unknown as Vite.ViteDevServer;
 }
@@ -48,10 +57,14 @@ function fakeViteResolving(
 	resolvedIds: Record<string, string>
 ): Vite.ViteDevServer {
 	return {
-		pluginContainer: {
-			resolveId: async (specifier: string) => {
-				const id = resolvedIds[specifier];
-				return id === undefined ? null : { id };
+		environments: {
+			ssr: {
+				pluginContainer: {
+					resolveId: async (specifier: string) => {
+						const id = resolvedIds[specifier];
+						return id === undefined ? null : { id };
+					},
+				},
 			},
 		},
 	} as unknown as Vite.ViteDevServer;