diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 86f2825..7074674 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -66,6 +66,32 @@ jobs:
       - run: npm ci --ignore-scripts
       - run: npm run test:unit
 
+  smoke:
+    name: Smoke test on Node.js ${{ matrix.node-version }} @ ${{ matrix.os }}
+    needs: build
+    strategy:
+      fail-fast: false
+      matrix:
+        node-version:
+          - 18.0.0
+          - 18.x
+        os: [ubuntu-latest, windows-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - name: Use Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7.0.0
+        with:
+          node-version: ${{ matrix.node-version }}
+      - uses: actions/download-artifact@v8
+        with:
+          name: dist
+          path: dist/
+      # No `npm ci` on purpose: the smoke test imports `dist/` and node
+      # builtins only. Installing dev dependencies is what made 18.x
+      # unworkable before, so this job never touches them.
+      - run: npm run test:smoke
+
   bun-build:
     name: Build on Bun (latest) @ ubuntu-latest
     runs-on: ubuntu-latest
diff --git a/package.json b/package.json
index a1cb01e..556f759 100644
--- a/package.json
+++ b/package.json
@@ -19,7 +19,8 @@
     "lint": "tsc --noEmit && eslint src && publint",
     "prepare": "npm run build",
     "test": "npm run build && npm run test:unit",
-    "test:unit": "vitest run"
+    "test:unit": "vitest run",
+    "test:smoke": "node test/smoke.mjs"
   },
   "repository": {
     "type": "git",
diff --git a/test/smoke.mjs b/test/smoke.mjs
new file mode 100644
index 0000000..5ae9fae
--- /dev/null
+++ b/test/smoke.mjs
@@ -0,0 +1,147 @@
+// A dependency-free smoke test for the built output, run against Node.js
+// versions that the dev stack no longer supports (see #57).
+//
+// Everything here is deliberately plain: `node:assert` and a `for` loop, no
+// test runner and no `node_modules`. Vitest, tsdown and the node test runner
+// all fail or flake on 18.x, which is what made the previous attempt at this
+// stall (#109) — importing `dist/` and nothing else is the one approach that
+// does not drag the toolchain along.
+//
+// It covers the happy path only. The exhaustive suite runs on supported
+// versions; this exists to prove the published bundle still imports and runs
+// where `engines.node` claims it does.
+
+import assert from 'node:assert';
+import {x, xSync, exec, execSync, NonZeroExitError} from '../dist/main.mjs';
+
+// `process.execPath` keeps every case shell- and platform-independent, so the
+// same file runs unmodified on Windows.
+const node = process.execPath;
+
+const tests = [];
+function test(name, fn) {
+  tests.push({name, fn});
+}
+
+test('x() captures stdout and a zero exit code', async () => {
+  const proc = x(node, ['-e', 'process.stdout.write("hello")']);
+  const result = await proc;
+
+  assert.strictEqual(result.stdout, 'hello');
+  assert.strictEqual(result.stderr, '');
+  assert.strictEqual(result.exitCode, 0);
+  assert.strictEqual(proc.exitCode, 0);
+  assert.strictEqual(proc.signalCode, null);
+});
+
+test('x() captures stderr', async () => {
+  const result = await x(node, ['-e', 'process.stderr.write("oh no")']);
+
+  assert.strictEqual(result.stdout, '');
+  assert.strictEqual(result.stderr, 'oh no');
+});
+
+test('x() forwards arguments verbatim', async () => {
+  const result = await x(node, [
+    '-e',
+    'process.stdout.write(process.argv.slice(1).join("|"))',
+    'one',
+    'two three'
+  ]);
+
+  assert.strictEqual(result.stdout, 'one|two three');
+});
+
+test('x() is async-iterable over output lines', async () => {
+  const lines = [];
+  for await (const line of x(node, [
+    '-e',
+    'console.log("first"); console.log("second")'
+  ])) {
+    lines.push(line);
+  }
+
+  assert.deepStrictEqual(lines, ['first', 'second']);
+});
+
+test('x() reports a non-zero exit code without throwing by default', async () => {
+  const result = await x(node, ['-e', 'process.exit(3)']);
+
+  assert.strictEqual(result.exitCode, 3);
+});
+
+test('x() throws NonZeroExitError when throwOnError is set', async () => {
+  // `x()` returns a PromiseLike, not a Promise, so it is awaited inside an
+  // async function rather than handed to assert.rejects directly.
+  await assert.rejects(
+    async () => {
+      await x(node, ['-e', 'process.exit(3)'], {throwOnError: true});
+    },
+    (err) => {
+      assert.ok(
+        err instanceof NonZeroExitError,
+        `expected a NonZeroExitError, got ${err && err.constructor.name}`
+      );
+      assert.strictEqual(err.exitCode, 3);
+      return true;
+    }
+  );
+});
+
+test('x() passes env through to the child', async () => {
+  const result = await x(node, ['-e', 'process.stdout.write(process.env.SMOKE)'], {
+    nodeOptions: {env: {SMOKE: 'value'}}
+  });
+
+  assert.strictEqual(result.stdout, 'value');
+});
+
+test('xSync() captures stdout and a zero exit code', () => {
+  const result = xSync(node, ['-e', 'process.stdout.write("hello sync")']);
+
+  assert.strictEqual(result.stdout, 'hello sync');
+  assert.strictEqual(result.exitCode, 0);
+});
+
+test('xSync() throws NonZeroExitError when throwOnError is set', () => {
+  assert.throws(
+    () => xSync(node, ['-e', 'process.exit(4)'], {throwOnError: true}),
+    (err) => {
+      assert.ok(
+        err instanceof NonZeroExitError,
+        `expected a NonZeroExitError, got ${err && err.constructor.name}`
+      );
+      assert.strictEqual(err.exitCode, 4);
+      return true;
+    }
+  );
+});
+
+test('exec and execSync are exported as aliases', () => {
+  assert.strictEqual(exec, x);
+  assert.strictEqual(execSync, xSync);
+});
+
+const failures = [];
+
+for (const {name, fn} of tests) {
+  try {
+    await fn();
+    console.log(`ok - ${name}`);
+  } catch (err) {
+    failures.push({name, err});
+    console.log(`not ok - ${name}`);
+  }
+}
+
+console.log(`\n${tests.length - failures.length}/${tests.length} passed`);
+
+if (failures.length > 0) {
+  for (const {name, err} of failures) {
+    console.error(`\n${name}:`);
+    console.error(err);
+  }
+  process.exit(1);
+}
+
+console.log(`smoke test passed on Node.js ${process.version}`);