diff --git a/nginx/default.conf b/nginx/default.conf
index ae92bbe..70cd90f 100644
--- a/nginx/default.conf
+++ b/nginx/default.conf
@@ -12,7 +12,7 @@ server {
     location ^~ /tts/piper-wasm-v1/ {
         types {
             application/wasm wasm;
-            application/javascript js;
+            application/javascript js mjs;
             application/json json;
             application/octet-stream onnx;
             text/plain txt;
diff --git a/piper-onnx-config.mjs b/piper-onnx-config.mjs
new file mode 100644
index 0000000..03313dc
--- /dev/null
+++ b/piper-onnx-config.mjs
@@ -0,0 +1,7 @@
+const assetRoot = '/tts/piper-wasm-v1/onnx/';
+
+export function createOnnxWasmPaths(origin) {
+  const absoluteAssetRoot = new URL(assetRoot, origin).href;
+  return absoluteAssetRoot;
+}
+
diff --git a/piper-worker.js b/piper-worker.js
index 5ff91a4..116d559 100644
--- a/piper-worker.js
+++ b/piper-worker.js
@@ -1,5 +1,6 @@
 import {TtsSession} from '@mintplex-labs/piper-tts-web';
 import {localPiperModelUrl} from './piper-model-routing.mjs';
+import {createOnnxWasmPaths} from './piper-onnx-config.mjs';
 
 const VOICE_ID = 'sv_SE-nst-medium';
 const ASSET_ROOT = '/tts/piper-wasm-v1';
@@ -24,7 +25,7 @@ async function getSession(onProgress) {
       voiceId: VOICE_ID,
       progress: onProgress,
       wasmPaths: {
-        onnxWasm: `${ASSET_ROOT}/onnx/`,
+        onnxWasm: createOnnxWasmPaths(self.location.origin),
         piperData: `${ASSET_ROOT}/piper/piper_phonemize.data`,
         piperWasm: `${ASSET_ROOT}/piper/piper_phonemize.wasm`,
       },
diff --git a/scripts/build-piper.mjs b/scripts/build-piper.mjs
index 71e15a3..e0cb93f 100644
--- a/scripts/build-piper.mjs
+++ b/scripts/build-piper.mjs
@@ -64,10 +64,16 @@ await mkdir(join(assetRoot, 'piper'), {recursive: true});
 for (const file of voiceFiles) await downloadVoiceFile(file);
 await cp(join(root, 'PIPER_VOICE_NOTICES.txt'), join(assetRoot, 'voices', 'ATTRIBUTION.txt'));
 
-const wasmFiles = (await readdir(onnxSource))
-  .filter(name => name.endsWith('.wasm'));
-if (wasmFiles.length === 0) throw new Error('ONNX Runtime WebAssembly files are missing');
-for (const file of wasmFiles) {
+const onnxRuntimeFiles = (await readdir(onnxSource))
+  .filter(name => name.endsWith('.wasm') || name.endsWith('.mjs'));
+const requiredOnnxRuntimeFiles = [
+  'ort-wasm-simd-threaded.wasm',
+  'ort-wasm-simd-threaded.mjs',
+];
+for (const file of requiredOnnxRuntimeFiles) {
+  if (!onnxRuntimeFiles.includes(file)) throw new Error(`Missing ONNX Runtime asset: ${file}`);
+}
+for (const file of onnxRuntimeFiles) {
   await cp(join(onnxSource, file), join(assetRoot, 'onnx', file));
 }
 for (const file of [piperWasm, piperData]) {
@@ -106,7 +112,8 @@ for (const file of voiceFiles) {
 }
 const workerBundle = await (await import('node:fs/promises')).readFile(join(assetRoot, 'piper-worker.js'), 'utf8');
 if (!workerBundle.includes('https://huggingface.co/diffusionstudio/piper-voices/resolve/main/') ||
-    !workerBundle.includes('/tts/piper-wasm-v1/voices/')) {
+    !workerBundle.includes('/tts/piper-wasm-v1/voices/') ||
+    !workerBundle.includes('/tts/piper-wasm-v1/onnx/')) {
   throw new Error('The Piper worker is missing its same-origin model download route.');
 }
 
diff --git a/scripts/check-frontend.sh b/scripts/check-frontend.sh
index bbff805..4ba0b3f 100755
--- a/scripts/check-frontend.sh
+++ b/scripts/check-frontend.sh
@@ -11,6 +11,7 @@ grep -q 'Cross-Origin-Embedder-Policy "require-corp"' nginx/default.conf
 grep -q 'add_header Cross-Origin-Embedder-Policy "require-corp" always;' nginx/default.conf
 grep -q 'add_header Cross-Origin-Resource-Policy "same-origin" always;' nginx/default.conf
 grep -q 'application/javascript js;' nginx/default.conf
+grep -q 'application/javascript js mjs;' nginx/default.conf
 grep -q "request('/version')" index.html
 grep -Fq "credentials: 'same-origin'" index.html
 grep -q 'id="dialogue" aria-label="Dialoghistorik" role="log" aria-live="polite"' index.html
@@ -47,6 +48,9 @@ grep -q 'new Worker(workerUrl)' piper-runtime.js
 grep -q 'worker.js?v=' piper-runtime.js
 grep -q 'worker.onmessageerror' piper-runtime.js
 grep -q 'localPiperModelUrl' piper-worker.js
+grep -q 'createOnnxWasmPaths(self.location.origin)' piper-worker.js
+grep -q 'ort-wasm-simd-threaded.mjs' scripts/build-piper.mjs
+grep -q 'ort-wasm-simd-threaded.wasm' scripts/build-piper.mjs
 grep -q 'PIPER_MODEL_ORIGIN' piper-model-routing.mjs
 grep -q '/tts/piper-wasm-v1/voices/' piper-model-routing.mjs
 grep -q 'same-origin.*voice' README.md
diff --git a/tests/piper-onnx-config.test.cjs b/tests/piper-onnx-config.test.cjs
new file mode 100644
index 0000000..1e78094
--- /dev/null
+++ b/tests/piper-onnx-config.test.cjs
@@ -0,0 +1,15 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+
+test('ONNX Runtime receives an absolute same-origin base URL', async () => {
+  const {createOnnxWasmPaths} = await import('../piper-onnx-config.mjs');
+  const wasmPaths = createOnnxWasmPaths('https://ai-spel.k3s.k0.nu');
+  assert.equal(wasmPaths, 'https://ai-spel.k3s.k0.nu/tts/piper-wasm-v1/onnx/');
+  assert.equal(new URL('ort-wasm-simd-threaded.mjs', wasmPaths).href,
+    'https://ai-spel.k3s.k0.nu/tts/piper-wasm-v1/onnx/ort-wasm-simd-threaded.mjs');
+});
+
+test('ONNX Runtime base URL rejects an invalid worker origin', async () => {
+  const {createOnnxWasmPaths} = await import('../piper-onnx-config.mjs');
+  assert.throws(() => createOnnxWasmPaths('undefined'), TypeError);
+});