diff --git a/docs/guide/migration.md b/docs/guide/migration.md
index d10de506ce3c..17d52b49c4fb 100644
--- a/docs/guide/migration.md
+++ b/docs/guide/migration.md
@@ -14,6 +14,19 @@ Jest has their [globals API](https://jestjs.io/docs/api) enabled by default. Vit
 
 If you decide to keep globals disabled, be aware that common libraries like [`testing-library`](https://testing-library.com/) will not run auto DOM [cleanup](https://testing-library.com/docs/svelte-testing-library/api/#cleanup).
 
+**Module mocks**
+
+When mocking a module in Jest, the factory argument's return value is the default export. In Vitest, the factory argument has to return an object with each export explicitly defined. For example, the following `jest.mock` would have to be updated as follows:
+
+```diff
+- jest.mock('./some-path', () => 'hello')
++ vi.mock('./some-path', () => ({
++   default: 'hello',
++ })
+```
+
+For more details please refer to the [vi.mock api](/api/#vi-mock)
+
 **Auto-Mocking Behaviour**
 
 Unlike Jest, mocked modules in `<root>/__mocks__` are not loaded unless `vi.mock()` is called. If you need them to be mocked in every test, like in Jest, you can mock them inside [`setupFiles`](/config/#setupfiles).
diff --git a/examples/mocks/test/factory.test.ts b/examples/mocks/test/factory.test.ts
index 0cf1822ebf0a..1567d88efe10 100644
--- a/examples/mocks/test/factory.test.ts
+++ b/examples/mocks/test/factory.test.ts
@@ -7,6 +7,7 @@ vi
   .mock('../src/example', () => ({
     mocked: true,
     then: 'a then export',
+    ok: undefined,
     square: (a: any, b: any) => a + b,
     asyncSquare: async (a: any, b: any) => Promise.resolve(a + b),
   }))
@@ -60,6 +61,7 @@ describe('mocking with factory', () => {
   })
 
   test('defined exports on mock', async () => {
+    expect((example as any).ok).toBe(undefined)
     expect((example as any).then).toBe('a then export')
     expect((example as any).mocked).toBe(true)
     expect(example.square(2, 3)).toBe(5)
diff --git a/packages/vitest/src/runtime/mocker.ts b/packages/vitest/src/runtime/mocker.ts
index 7361cbff8741..d2105de179c3 100644
--- a/packages/vitest/src/runtime/mocker.ts
+++ b/packages/vitest/src/runtime/mocker.ts
@@ -122,7 +122,7 @@ export class VitestMocker {
           if (target instanceof Promise)
             return target.then.bind(target)
         }
-        else if (val === undefined) {
+        else if (!(prop in target)) {
           throw new Error(`[vitest] No "${prop}" export is defined on the "${dep}"`)
         }