diff --git a/tests/sitemap-index.test.ts b/tests/sitemap-index.test.ts
index 8a207c9..525fb28 100644
--- a/tests/sitemap-index.test.ts
+++ b/tests/sitemap-index.test.ts
@@ -1,6 +1,6 @@
 import { SitemapStream } from '../index';
 import { tmpdir } from 'os';
-import { resolve, join } from 'path';
+import { join, resolve } from 'path';
 import {
   existsSync,
   unlinkSync,
@@ -11,9 +11,9 @@ import {
   SitemapIndexStream,
   SitemapAndIndexStream,
 } from '../lib/sitemap-index-stream';
-import { streamToPromise } from '../dist';
+import { streamToPromise } from '../lib/sitemap-stream';
 import { finished as finishedCallback } from 'stream';
-import { WriteStream } from 'node:fs';
+import { readFileSync, WriteStream } from 'node:fs';
 import { promisify } from 'util';
 
 const finished = promisify(finishedCallback);
@@ -134,6 +134,8 @@ describe('sitemapAndIndex', () => {
       resolve(targetFolder, `./sitemap-1.xml`),
       resolve(targetFolder, `./sitemap-2.xml`),
       resolve(targetFolder, `./sitemap-3.xml`),
+      resolve(targetFolder, `./sitemap-4.xml`),
+      resolve(targetFolder, `./sitemap-index.xml`),
     ]);
   });
 
@@ -143,6 +145,8 @@ describe('sitemapAndIndex', () => {
       resolve(targetFolder, `./sitemap-1.xml`),
       resolve(targetFolder, `./sitemap-2.xml`),
       resolve(targetFolder, `./sitemap-3.xml`),
+      resolve(targetFolder, `./sitemap-4.xml`),
+      resolve(targetFolder, `./sitemap-index.xml`),
     ]);
   });
 
@@ -155,7 +159,15 @@ describe('sitemapAndIndex', () => {
         const sm = new SitemapStream();
         const path = `./sitemap-${i}.xml`;
 
-        const ws = sm.pipe(createWriteStream(resolve(targetFolder, path)));
+        const outputStream = createWriteStream(resolve(targetFolder, path));
+
+        // Streams do not automatically propagate errors
+        // We must propagate this up to the SitemapStream
+        outputStream.on('error', (err) => {
+          sm.emit('error', err);
+        });
+
+        const ws = sm.pipe(outputStream);
         return [new URL(path, baseURL).toString(), sm, ws];
       },
     });
@@ -222,4 +234,292 @@ describe('sitemapAndIndex', () => {
       )
     ).toBe(false);
   });
+
+  it('writes to index file', async () => {
+    const baseURL = 'https://example.com/sub/';
+
+    const sms = new SitemapAndIndexStream({
+      limit: 2,
+      getSitemapStream: (i: number): [string, SitemapStream, WriteStream] => {
+        const sm = new SitemapStream();
+        const path = `./sitemap-${i}.xml`;
+
+        // This will not throw even though it will fail
+        // `outputStream.writable === true`
+        // `outputStream.closed === false`
+        const outputStream = createWriteStream(resolve(targetFolder, path));
+
+        // Streams do not automatically propagate errors
+        // We must propagate this up to the SitemapStream
+        outputStream.on('error', (err) => {
+          sm.emit('error', err);
+        });
+
+        const ws = sm.pipe(outputStream);
+        return [new URL(path, baseURL).toString(), sm, ws];
+      },
+    });
+
+    // Pipe the index stream to a file
+    const indexStream = createWriteStream(
+      resolve(targetFolder, `./sitemap-index.xml`)
+    );
+    sms.pipe(indexStream);
+    await writeData(sms, 'https://1.example.com/a');
+    await writeData(sms, 'https://2.example.com/a');
+    await writeData(sms, 'https://3.example.com/a');
+    sms.end();
+    await expect(finished(sms)).resolves.toBeUndefined();
+
+    await finished(indexStream);
+
+    expect(existsSync(resolve(targetFolder, `./sitemap-index.xml`))).toBe(true);
+    expect(existsSync(resolve(targetFolder, `./sitemap-0.xml`))).toBe(true);
+    expect(existsSync(resolve(targetFolder, `./sitemap-1.xml`))).toBe(true);
+    expect(existsSync(resolve(targetFolder, `./sitemap-2.xml`))).toBe(false);
+
+    // Read the first sitemap to make sure it was written
+    const sitemap0 = await streamToPromise(
+      createReadStream(resolve(targetFolder, `./sitemap-0.xml`))
+    );
+    expect(sitemap0.toString()).toContain('https://1.example.com/a');
+
+    // Read the last sitemap to make sure it was written
+    const sitemap1 = await streamToPromise(
+      createReadStream(resolve(targetFolder, `./sitemap-1.xml`))
+    );
+    expect(sitemap1.toString()).toContain('https://3.example.com/a');
+
+    // Read the index to make sure it was written
+    const indexText = readFileSync(
+      resolve(targetFolder, `./sitemap-index.xml`),
+      'utf-8'
+    );
+    expect(indexText).toContain(`${baseURL}sitemap-0`);
+    expect(indexText).toContain(`${baseURL}sitemap-1`);
+    expect(indexText).not.toContain(`${baseURL}sitemap-2`);
+  });
+
+  it('does not hang if last sitemap is filled', async () => {
+    const baseURL = 'https://example.com/sub/';
+
+    const sms = new SitemapAndIndexStream({
+      limit: 2,
+      getSitemapStream: (i: number): [string, SitemapStream, WriteStream] => {
+        const sm = new SitemapStream();
+        const path = `./sitemap-${i}.xml`;
+
+        // This will not throw even though it will fail
+        // `outputStream.writable === true`
+        // `outputStream.closed === false`
+        const outputStream = createWriteStream(resolve(targetFolder, path));
+
+        // Streams do not automatically propagate errors
+        // We must propagate this up to the SitemapStream
+        outputStream.on('error', (err) => {
+          sm.emit('error', err);
+        });
+
+        const ws = sm.pipe(outputStream);
+        return [new URL(path, baseURL).toString(), sm, ws];
+      },
+    });
+
+    // Pipe the index stream to a file
+    const indexStream = createWriteStream(
+      resolve(targetFolder, `./sitemap-index.xml`)
+    );
+    sms.pipe(indexStream);
+    await writeData(sms, 'https://1.example.com/a');
+    await writeData(sms, 'https://2.example.com/a');
+    sms.end();
+    await expect(finished(sms)).resolves.toBeUndefined();
+
+    await finished(indexStream);
+
+    expect(existsSync(resolve(targetFolder, `./sitemap-index.xml`))).toBe(true);
+    expect(existsSync(resolve(targetFolder, `./sitemap-0.xml`))).toBe(true);
+    expect(existsSync(resolve(targetFolder, `./sitemap-1.xml`))).toBe(false);
+
+    const sitemap0Raw = readFileSync(
+      resolve(targetFolder, `./sitemap-0.xml`),
+      'utf-8'
+    );
+    expect(sitemap0Raw).toContain('https://1.example.com/a');
+    expect(sitemap0Raw).toContain('https://2.example.com/a');
+    expect(sitemap0Raw).not.toContain('https://3.example.com/a');
+
+    // Read the first sitemap to make sure it was written
+    const sitemap0 = await streamToPromise(
+      createReadStream(resolve(targetFolder, `./sitemap-0.xml`))
+    );
+    expect(sitemap0.toString()).toContain('https://1.example.com/a');
+
+    // Read the index to make sure it was written
+    const indexText = readFileSync(
+      resolve(targetFolder, `./sitemap-index.xml`),
+      'utf-8'
+    );
+    expect(indexText).toContain(`${baseURL}sitemap-0`);
+    expect(indexText).not.toContain(`${baseURL}sitemap-1`);
+  });
+
+  it('deterministically finishes writing each sitemap file before creating a new one', async () => {
+    const baseURL = 'https://example.com/sub/';
+
+    const sms = new SitemapAndIndexStream({
+      limit: 5000,
+      getSitemapStream: (i: number): [string, SitemapStream, WriteStream] => {
+        const sm = new SitemapStream();
+        const path = `./sitemap-${i}.xml`;
+
+        // This will not throw even though it will fail
+        // `outputStream.writable === true`
+        // `outputStream.closed === false`
+        const outputStream = createWriteStream(resolve(targetFolder, path));
+
+        // Streams do not automatically propagate errors
+        // We must propagate this up to the SitemapStream
+        outputStream.on('error', (err) => {
+          sm.emit('error', err);
+        });
+
+        const ws = sm.pipe(outputStream);
+        return [new URL(path, baseURL).toString(), sm, ws];
+      },
+    });
+
+    // Pipe the index stream to a file
+    const indexStream = createWriteStream(
+      resolve(targetFolder, `./sitemap-index.xml`)
+    );
+    sms.pipe(indexStream);
+    for (let i = 0; i < 5000; i++) {
+      // Intentionally write while ignoring back pressure to stress test
+      // the rolling to new files
+      sms.write(`https://1.example.com/a${i}`);
+    }
+    for (let i = 0; i < 5000; i++) {
+      sms.write(`https://2.example.com/a${i}`);
+    }
+    for (let i = 0; i < 1; i++) {
+      sms.write(`https://3.example.com/a${i}`);
+    }
+    sms.end();
+    await expect(finished(sms)).resolves.toBeUndefined();
+
+    await finished(indexStream);
+
+    expect(existsSync(resolve(targetFolder, `./sitemap-index.xml`))).toBe(true);
+    expect(existsSync(resolve(targetFolder, `./sitemap-0.xml`))).toBe(true);
+    expect(existsSync(resolve(targetFolder, `./sitemap-1.xml`))).toBe(true);
+    expect(existsSync(resolve(targetFolder, `./sitemap-2.xml`))).toBe(true);
+    expect(existsSync(resolve(targetFolder, `./sitemap-3.xml`))).toBe(false);
+
+    // Make sure the very first file is completed
+    const sitemap0Raw = readFileSync(
+      resolve(targetFolder, `./sitemap-0.xml`),
+      'utf-8'
+    );
+    expect(sitemap0Raw).toContain('</urlset>');
+    expect(sitemap0Raw).toContain('https://1.example.com/a0');
+    expect(sitemap0Raw).toContain('https://1.example.com/a4999');
+    expect(sitemap0Raw).toContain('</urlset>');
+
+    // Make sure the first rolled file is completed
+    const sitemap1Raw = readFileSync(
+      resolve(targetFolder, `./sitemap-1.xml`),
+      'utf-8'
+    );
+    expect(sitemap1Raw).toContain('</urlset>');
+    expect(sitemap1Raw).toContain('https://2.example.com/a0');
+    expect(sitemap1Raw).toContain('https://2.example.com/a4999');
+    expect(sitemap1Raw).toContain('</urlset>');
+
+    // Make sure the last file is completed
+    const sitemap2Raw = readFileSync(
+      resolve(targetFolder, `./sitemap-2.xml`),
+      'utf-8'
+    );
+    expect(sitemap2Raw).toContain('</urlset>');
+    expect(sitemap2Raw).toContain('https://3.example.com/a0');
+    expect(sitemap2Raw).toContain('</urlset>');
+    expect(sitemap2Raw).not.toContain('https://3.example.com/a1');
+
+    // Read the index to make sure it was written
+    const indexText = readFileSync(
+      resolve(targetFolder, `./sitemap-index.xml`),
+      'utf-8'
+    );
+    expect(indexText).toContain('<sitemapindex');
+    expect(indexText).toContain(`${baseURL}sitemap-0`);
+    expect(indexText).toContain(`${baseURL}sitemap-1`);
+    expect(indexText).toContain(`${baseURL}sitemap-2`);
+    expect(indexText).toContain('</sitemapindex>');
+    expect(indexText).not.toContain(`${baseURL}sitemap-3`);
+  });
+
+  it('works if no items written at all', async () => {
+    const baseURL = 'https://example.com/sub/';
+
+    const sms = new SitemapAndIndexStream({
+      limit: 2,
+      getSitemapStream: (i: number): [string, SitemapStream, WriteStream] => {
+        const sm = new SitemapStream();
+        const path = `./sitemap-${i}.xml`;
+
+        // This will not throw even though it will fail
+        // `outputStream.writable === true`
+        // `outputStream.closed === false`
+        const outputStream = createWriteStream(resolve(targetFolder, path));
+
+        // Streams do not automatically propagate errors
+        // We must propagate this up to the SitemapStream
+        outputStream.on('error', (err) => {
+          sm.emit('error', err);
+        });
+
+        const ws = sm.pipe(outputStream);
+        return [new URL(path, baseURL).toString(), sm, ws];
+      },
+    });
+
+    // Pipe the index stream to a file
+    const indexStream = createWriteStream(
+      resolve(targetFolder, `./sitemap-index.xml`)
+    );
+    sms.pipe(indexStream);
+    sms.end();
+    await expect(finished(sms)).resolves.toBeUndefined();
+
+    await finished(indexStream);
+
+    expect(existsSync(resolve(targetFolder, `./sitemap-index.xml`))).toBe(true);
+    expect(existsSync(resolve(targetFolder, `./sitemap-0.xml`))).toBe(false);
+
+    // Read the first sitemap to make sure it was NOT written
+    await expect(
+      streamToPromise(
+        createReadStream(resolve(targetFolder, `./sitemap-0.xml`))
+      )
+    ).rejects.toThrow('ENOENT');
+
+    // Read the index to make sure it was written
+    const indexText = readFileSync(
+      resolve(targetFolder, `./sitemap-index.xml`),
+      'utf-8'
+    );
+    expect(indexText).toContain(`${baseURL}sitemap-0`);
+    expect(indexText).toContain(`${baseURL}sitemap-1`);
+    expect(indexText).not.toContain(`${baseURL}sitemap-2`);
+  });
 });
+
+function writeData(sms: SitemapStream, data: any): Promise<void> {
+  if (!sms.write(data)) {
+    return new Promise((resolve) => {
+      sms.once('drain', resolve);
+    });
+  }
+  return Promise.resolve();
+}