diff --git a/packages/vitest/src/node/plugins/index.ts b/packages/vitest/src/node/plugins/index.ts
index 06eb1d2037da..29a2b1d467f0 100644
--- a/packages/vitest/src/node/plugins/index.ts
+++ b/packages/vitest/src/node/plugins/index.ts
@@ -103,7 +103,7 @@ export async function VitestPlugin(options: UserConfig = {}, ctx = new Vitest('t
                 isolate: options.poolOptions?.threads?.isolate ?? options.isolate ?? testConfig.poolOptions?.threads?.isolate ?? viteConfig.test?.isolate,
               },
               forks: {
-                isolate: options.poolOptions?.threads?.isolate ?? options.isolate ?? testConfig.poolOptions?.threads?.isolate ?? viteConfig.test?.isolate,
+                isolate: options.poolOptions?.forks?.isolate ?? options.isolate ?? testConfig.poolOptions?.forks?.isolate ?? viteConfig.test?.isolate,
               },
             },
           },
diff --git a/test/config/fixtures/pool-isolation/isolated.test.ts b/test/config/fixtures/pool-isolation/isolated.test.ts
new file mode 100644
index 000000000000..c0a0ab9148b6
--- /dev/null
+++ b/test/config/fixtures/pool-isolation/isolated.test.ts
@@ -0,0 +1,17 @@
+import { expect, test } from 'vitest'
+import type { UserConfig } from 'vitest/config'
+
+const pool = process.env.TESTED_POOL as "forks" | "threads";
+
+test('is isolated', () => {
+  // @ts-expect-error -- internal
+  const config: NonNullable<UserConfig['test']> = globalThis.__vitest_worker__.config
+
+  if (pool === 'forks') {
+    expect(config.poolOptions?.forks?.isolate).toBe(true)
+  }
+  else {
+    expect(pool).toBe('threads')
+    expect(config.poolOptions?.threads?.isolate).toBe(true)
+  }
+})
diff --git a/test/config/fixtures/pool-isolation/non-isolated.test.ts b/test/config/fixtures/pool-isolation/non-isolated.test.ts
new file mode 100644
index 000000000000..3a6471b9e657
--- /dev/null
+++ b/test/config/fixtures/pool-isolation/non-isolated.test.ts
@@ -0,0 +1,17 @@
+import { expect, test } from 'vitest'
+import type { UserConfig } from 'vitest/config'
+
+const pool = process.env.TESTED_POOL as "forks" | "threads";
+
+test('is isolated', () => {
+  // @ts-expect-error -- internal
+  const config: NonNullable<UserConfig['test']> = globalThis.__vitest_worker__.config
+
+  if (pool === 'forks') {
+    expect(config.poolOptions?.forks?.isolate).toBe(false)
+  }
+  else {
+    expect(pool).toBe('threads')
+    expect(config.poolOptions?.threads?.isolate).toBe(false)
+  }
+})
diff --git a/test/config/test/pool-isolation.test.ts b/test/config/test/pool-isolation.test.ts
new file mode 100644
index 000000000000..1d72f4d9e91c
--- /dev/null
+++ b/test/config/test/pool-isolation.test.ts
@@ -0,0 +1,72 @@
+import { describe, expect, test } from 'vitest'
+import { runVitest } from '../../test-utils'
+
+describe.each(['forks', 'threads'] as const)('%s', async (pool) => {
+  test('is isolated', async () => {
+    const { stderr, exitCode } = await runVitest({
+      root: './fixtures/pool-isolation',
+      include: ['isolated.test.ts'],
+      pool,
+      poolOptions: {
+        // Use default value on the tested pool and disable on the other one
+        [invertPool(pool)]: { isolate: false },
+      },
+      env: { TESTED_POOL: pool },
+    })
+
+    expect(stderr).toBe('')
+    expect(exitCode).toBe(0)
+  })
+
+  test('is isolated + poolMatchGlobs', async () => {
+    const { stderr, exitCode } = await runVitest({
+      root: './fixtures/pool-isolation',
+      include: ['isolated.test.ts'],
+      pool,
+      poolMatchGlobs: [['**', pool]],
+      poolOptions: {
+        // Use default value on the tested pool and disable on the other one
+        [invertPool(pool)]: { isolate: false },
+      },
+      env: { TESTED_POOL: pool },
+    })
+
+    expect(stderr).toBe('')
+    expect(exitCode).toBe(0)
+  })
+
+  test('is not isolated', async () => {
+    const { stderr, exitCode } = await runVitest({
+      root: './fixtures/pool-isolation',
+      include: ['non-isolated.test.ts'],
+      pool,
+      poolOptions: {
+        [pool]: { isolate: false },
+      },
+      env: { TESTED_POOL: pool },
+    })
+
+    expect(stderr).toBe('')
+    expect(exitCode).toBe(0)
+  })
+
+  test('is not isolated + poolMatchGlobs', async () => {
+    const { stderr, exitCode } = await runVitest({
+      root: './fixtures/pool-isolation',
+      include: ['non-isolated.test.ts'],
+      pool: invertPool(pool),
+      poolMatchGlobs: [['**/**.test.ts', pool]],
+      poolOptions: {
+        [pool]: { isolate: false },
+      },
+      env: { TESTED_POOL: pool },
+    })
+
+    expect(stderr).toBe('')
+    expect(exitCode).toBe(0)
+  })
+})
+
+function invertPool(pool: 'threads' | 'forks') {
+  return pool === 'threads' ? 'forks' : 'threads'
+}