diff --git a/.github/workflows/test-slow.yml b/.github/workflows/test-slow.yml
new file mode 100644
index 0000000..797bf51
--- /dev/null
+++ b/.github/workflows/test-slow.yml
@@ -0,0 +1,22 @@
+name: Run slow JS tests
+on:
+  schedule:
+    - cron: '0 12 * * *'
+  workflow_dispatch:
+jobs:
+  big:
+    name: Test large inputs
+    runs-on: ubuntu-latest
+    env:
+      MSHOULD_FAST: ''
+    steps:
+      - uses: actions/checkout@1e31de5234b9f8995739874a8ce0492dc87873e2 # v4
+      - name: Use Node.js ${{ matrix.node }}
+        uses: actions/setup-node@8f152de45cc393bb48ce5d89d36b731f54556e65 # v4
+        with:
+          node-version: ${{ matrix.node }}
+          registry-url: 'https://registry.npmjs.org'
+          cache: npm
+      - run: npm install
+      - run: npm run build --if-present
+      - run: npm run test:big
diff --git a/test/crosstest.test.js b/test/crosstest.test.js
index 87feb21..e58c343 100644
--- a/test/crosstest.test.js
+++ b/test/crosstest.test.js
@@ -1,9 +1,9 @@
+import { describe, should } from 'micro-should';
 import { deepStrictEqual } from 'node:assert';
-import { getCiphers, createCipheriv, createDecipheriv } from 'node:crypto';
-import { should, describe } from 'micro-should';
+import { createCipheriv, createDecipheriv, getCiphers } from 'node:crypto';
 import * as aes from '../esm/aes.js';
+import { chacha20, chacha20poly1305, xchacha20poly1305 } from '../esm/chacha.js';
 import { xsalsa20poly1305 } from '../esm/salsa.js';
-import { chacha20poly1305, xchacha20poly1305, chacha20 } from '../esm/chacha.js';
 import { concatBytes } from '../esm/utils.js';
 
 const KB = 1024;
@@ -357,5 +357,4 @@ describe('Cross-test (node)', () => {
   }
 });
 
-if (SLOW) process.env.MSHOULD_FAST = '1'; // parallel
 should.runWhen(import.meta.url);