diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index f5c1797..2fe421c 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -12,6 +12,12 @@ jobs:
     strategy:
       matrix:
         node: [18, 20, 'lts/*']
+        os: [ubuntu-latest]
+        include:
+        - os: macos-latest
+          node: 'lts/*'
+        - os: windows-latest
+          node: 'lts/*'
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
diff --git a/.test.cjs b/.test.cjs
new file mode 100644
index 0000000..0511ac4
--- /dev/null
+++ b/.test.cjs
@@ -0,0 +1,11 @@
+const plugin = require('postcss-normalize');
+const postcss = require('postcss');
+const assert = require('node:assert');
+
+postcss([plugin()]).process('@import "sanitize.css"', { from: null }).then((result) => {
+	assert.ok(result.css.includes(':where('));
+});
+
+postcss([plugin()]).process('@import "normalize.css"', { from: null }).then((result) => {
+	assert.ok(result.css.includes(':where('));
+});
diff --git a/.test.mjs b/.test.mjs
new file mode 100644
index 0000000..c568447
--- /dev/null
+++ b/.test.mjs
@@ -0,0 +1,11 @@
+import plugin from 'postcss-normalize';
+import postcss from 'postcss';
+import assert from 'node:assert';
+
+postcss([plugin()]).process('@import "sanitize.css"', { from: null }).then((result) => {
+	assert.ok(result.css.includes(':where('));
+});
+
+postcss([plugin()]).process('@import "normalize.css"', { from: null }).then((result) => {
+	assert.ok(result.css.includes(':where('));
+});
diff --git a/package.json b/package.json
index 38195c9..3e73f02 100644
--- a/package.json
+++ b/package.json
@@ -23,7 +23,7 @@
   "scripts": {
     "prepublishOnly": "npm test",
     "build": "rollup --config .rollup.mjs --silent",
-    "test": "npm run build && npm run tape",
+    "test": "npm run build && npm run tape && node .test.cjs && node .test.mjs",
     "tape": "postcss-tape"
   },
   "engines": {