diff --git a/packages/vitest/src/node/pools/pool.ts b/packages/vitest/src/node/pools/pool.ts
index 13cc822e5..dd14bd48f 100644
--- a/packages/vitest/src/node/pools/pool.ts
+++ b/packages/vitest/src/node/pools/pool.ts
@@ -80,6 +80,8 @@ export class Pool {
       let isMemoryLimitReached = false
       const runner = this.getPoolRunner(task, method)
 
+      // `setMaxWorkers` can replace the map for the next group before this id is freed
+      const workerIds = this.workerIds
       const poolId = runner.poolId ?? this.getConcurrencyId()
       runner.poolId = poolId
 
@@ -195,7 +197,7 @@ export class Pool {
         )
       }
 
-      this.freeWorkerId(poolId)
+      workerIds.set(poolId, true)
     }
 
     // This is mostly to avoid zombie workers when/if Vitest internals run into errors
diff --git a/test/e2e/test/group-order.test.ts b/test/e2e/test/group-order.test.ts
index 4cb3d1a0d..158dff2b4 100644
--- a/test/e2e/test/group-order.test.ts
+++ b/test/e2e/test/group-order.test.ts
@@ -58,3 +58,82 @@ test('tests run according to the group order', async () => {
      ✓ |1| example.1.test.ts > 1 <time>"
   `)
 })
+
+test('the next group does not reuse a pool id that is still in use', async () => {
+  const uniquePoolId = /* ts */ `
+    import { mkdirSync, rmSync } from 'node:fs'
+    import { onTestFinished, test } from 'vitest'
+
+    test('unique pool id', async () => {
+      const locks = import.meta.dirname + '/../.locks'
+      mkdirSync(locks, { recursive: true })
+      const lock = locks + '/' + process.env.VITEST_POOL_ID
+      mkdirSync(lock)
+      onTestFinished(() => rmSync(lock, { recursive: true }))
+      await new Promise(resolve => setTimeout(resolve, 200))
+    })
+  `
+  const { stderr, testTree } = await runInlineTests(
+    {
+      // starts first with pool id 1 and finishes last in its group
+      'first/slow.test.ts': `test('slow', () => new Promise(resolve => setTimeout(resolve, 500)))`,
+      'first/fast-1.test.ts': `test('fast', () => {})`,
+      'first/fast-2.test.ts': `test('fast', () => {})`,
+      'first/fast-3.test.ts': `test('fast', () => {})`,
+      'second/1.test.ts': uniquePoolId,
+      'second/2.test.ts': uniquePoolId,
+      'second/3.test.ts': uniquePoolId,
+      'second/4.test.ts': uniquePoolId,
+    },
+    {
+      $cliOptions: { globals: true, maxWorkers: 4 },
+      projects: [
+        {
+          test: {
+            name: 'first',
+            include: ['./first/*.test.ts'],
+          },
+        },
+        {
+          test: {
+            name: 'second',
+            include: ['./second/*.test.ts'],
+            sequence: {
+              groupOrder: 1,
+            },
+          },
+        },
+      ],
+    },
+  )
+
+  expect(stderr).toBe('')
+  expect(testTree()).toMatchInlineSnapshot(`
+    {
+      "first/fast-1.test.ts": {
+        "fast": "passed",
+      },
+      "first/fast-2.test.ts": {
+        "fast": "passed",
+      },
+      "first/fast-3.test.ts": {
+        "fast": "passed",
+      },
+      "first/slow.test.ts": {
+        "slow": "passed",
+      },
+      "second/1.test.ts": {
+        "unique pool id": "passed",
+      },
+      "second/2.test.ts": {
+        "unique pool id": "passed",
+      },
+      "second/3.test.ts": {
+        "unique pool id": "passed",
+      },
+      "second/4.test.ts": {
+        "unique pool id": "passed",
+      },
+    }
+  `)
+})