diff --git a/.changeset/fix-bundler-worker-dataclone.md b/.changeset/fix-bundler-worker-dataclone.md
new file mode 100644
index 000000000..0ca6213df
--- /dev/null
+++ b/.changeset/fix-bundler-worker-dataclone.md
@@ -0,0 +1,6 @@
+---
+'@doc-kit/core': patch
+'@doc-kit/generator-react': patch
+---
+
+Exclude main-thread-only bundler options from worker thread configuration to prevent DataCloneError.
diff --git a/packages/core/src/generators/types.d.ts b/packages/core/src/generators/types.d.ts
index 7bac2a412..baf2edbcf 100644
--- a/packages/core/src/generators/types.d.ts
+++ b/packages/core/src/generators/types.d.ts
@@ -70,6 +70,9 @@ declare global {
 
     hasParallelProcessor?: boolean;
 
+    /** Configuration keys excluded from worker-thread messages. */
+    workerConfigOmit?: string[];
+
     /**
      * Receive the dependency's output as an async iterable of its chunks, as
      * they are produced, instead of one collected array. With one thread, the
diff --git a/packages/core/src/threading/__tests__/parallel.test.mjs b/packages/core/src/threading/__tests__/parallel.test.mjs
index 0f6cf1200..fee3194d0 100644
--- a/packages/core/src/threading/__tests__/parallel.test.mjs
+++ b/packages/core/src/threading/__tests__/parallel.test.mjs
@@ -302,6 +302,47 @@ describe('createParallelWorker', () => {
     deepStrictEqual(chunks, [[1, 2], [3, 4], [5]]);
   });
 
+  it('does not clone main-thread-only HTML bundler functions', async () => {
+    const htmlGenerator = await loadGenerator('html');
+    const transferred = [];
+    const pool = {
+      run(task) {
+        const copy = structuredClone(task);
+        transferred.push(copy);
+
+        return Promise.resolve(copy.input);
+      },
+    };
+    const bundler = {
+      buildServer: async () => 'file:///library.mjs',
+      buildClient: async () => ({}),
+      compile: async code => code,
+    };
+    const configuration = {
+      threads: 2,
+      chunkSize: 1,
+      html: { title: 'Worker regression test', bundler },
+    };
+    const worker = createParallelWorker(
+      'html',
+      htmlGenerator,
+      pool,
+      configuration
+    );
+    const results = await collectStream(worker.stream([1, 2, 3], {}));
+
+    deepStrictEqual(results, [1, 2, 3]);
+    strictEqual(transferred.length, 3);
+
+    for (const task of transferred) {
+      deepStrictEqual(task.configuration.html, {
+        title: 'Worker regression test',
+      });
+    }
+
+    strictEqual(configuration.html.bundler, bundler);
+  });
+
   describe('with streamed batches', () => {
     it(
       'starts a batch before the next one arrives',
diff --git a/packages/core/src/threading/parallel.mjs b/packages/core/src/threading/parallel.mjs
index 494264369..b6b22c1c1 100644
--- a/packages/core/src/threading/parallel.mjs
+++ b/packages/core/src/threading/parallel.mjs
@@ -1,7 +1,7 @@
 'use strict';
 
 import logger from '#logger/index.mjs';
-import { isAsyncIterable } from '#utils/misc.mjs';
+import { isAsyncIterable, omitKeys } from '#utils/misc.mjs';
 
 import { CHUNKS_PER_THREAD } from './constants.mjs';
 
@@ -76,7 +76,15 @@ export default function createParallelWorker(
 ) {
   const { threads, chunkSize } = configuration;
 
-  const { name } = generator;
+  const { name, workerConfigOmit } = generator;
+
+  const workerConfiguration =
+    workerConfigOmit?.length && configuration[name]
+      ? {
+          ...configuration,
+          [name]: omitKeys(configuration[name], workerConfigOmit),
+        }
+      : configuration;
 
   return {
     /**
@@ -165,7 +173,14 @@ export default function createParallelWorker(
           running++;
 
           const task = pool.run(
-            createTask(batch, indices, extra, configuration, specifier, name)
+            createTask(
+              batch,
+              indices,
+              extra,
+              workerConfiguration,
+              specifier,
+              name
+            )
           );
 
           tasks.push(
diff --git a/packages/react/src/html/index.mjs b/packages/react/src/html/index.mjs
index 607592a39..c3e48c583 100644
--- a/packages/react/src/html/index.mjs
+++ b/packages/react/src/html/index.mjs
@@ -96,5 +96,8 @@ export default {
   // page count, so it is farmed out to the worker pool.
   hasParallelProcessor: true,
 
+  // The bundler runs on the main thread and contains non-cloneable functions.
+  workerConfigOmit: ['bundler'],
+
   processChunk,
 };