--- a/third-party/include/ThreadPool.h
+++ b/third-party/include/ThreadPool.h
@@ -110,9 +110,20 @@
     : pool_size(threads)
     , in_flight(0)
 {
+#ifndef __EMSCRIPTEN__
     const std::unique_lock<std::mutex> lock(this->queue_mutex);
     for (std::size_t i = 0; i != threads; ++i)
         start_worker(i, lock);
+#else
+    // vpinball-wasm: a single-threaded Emscripten build (no -pthread /
+    // SharedArrayBuffer for v1) cannot construct real std::thread workers -
+    // std::thread's constructor throws at runtime otherwise ("thread
+    // constructor failed"). Run zero real workers; enqueue() below executes
+    // tasks synchronously and inline instead, matching the porting plan's
+    // "run ThreadPool work serially" decision for one-off parallel work
+    // (parallel .vpx item deserialization at load, env-map baking, etc.).
+    (void)pool_size;
+#endif
 }
 
 // add new work item to the pool
@@ -139,6 +150,15 @@
 
     std::future<return_type> res = task->get_future();
 
+#ifdef __EMSCRIPTEN__
+    // vpinball-wasm: no real worker threads exist (see the constructor) -
+    // run the task synchronously inline so callers still get a valid,
+    // already-ready future, exactly as if it had run on a worker.
+    (void)std::atomic_fetch_add_explicit(&in_flight, std::size_t(1), std::memory_order_relaxed);
+    (*task)();
+    (void)std::atomic_fetch_sub_explicit(&in_flight, std::size_t(1), std::memory_order_acq_rel);
+    return res;
+#else
     std::unique_lock<std::mutex> lock(queue_mutex);
     if (tasks.size () >= max_queue_size)
         // wait for the queue to empty or be stopped
@@ -160,6 +180,7 @@
     condition_consumers.notify_one();
 
     return res;
+#endif
 }