diff --git a/app/javascript/service-worker/build.js b/app/javascript/service-worker/build.js
index e4e087572..3eae2a591 100644
--- a/app/javascript/service-worker/build.js
+++ b/app/javascript/service-worker/build.js
@@ -56,7 +56,11 @@ function generateAssetManifest() {
 async function buildServiceWorker() {
   console.log('🔨 Building service worker...');
 
-  const assetOrigin = process.env.ASSET_CDN_HOST || '';
+  // Ensure CDN host has protocol prefix for absolute URLs
+  let assetOrigin = process.env.ASSET_CDN_HOST || '';
+  if (assetOrigin && !assetOrigin.startsWith('http')) {
+    assetOrigin = `https://${assetOrigin}`;
+  }
   const isProduction = process.env.NODE_ENV === 'production';
   // vite-plugin-ruby serves from /vite/ in production, /vite-dev/ in development
   const assetPath = isProduction ? '/vite/' : '/vite-dev/';
diff --git a/app/javascript/service-worker/sw-runtime.js b/app/javascript/service-worker/sw-runtime.js
index 695bbde55..9fa7a9c2c 100644
--- a/app/javascript/service-worker/sw-runtime.js
+++ b/app/javascript/service-worker/sw-runtime.js
@@ -123,7 +123,10 @@ async function prefetchAssets() {
   if (!ASSET_MANIFEST?.length) return;
 
   const cache = await caches.open(CACHE_NAME);
-  const baseUrl = ASSET_ORIGIN || `${self.location.origin}${ASSET_PATH}`;
+  // Build base URL: CDN origin + asset path, or local origin + asset path
+  const baseUrl = ASSET_ORIGIN
+    ? `${ASSET_ORIGIN}${ASSET_PATH}`
+    : `${self.location.origin}${ASSET_PATH}`;
 
   // Prefetch in batches of 5 (await in loop is intentional for throttling)
   for (let i = 0; i < ASSET_MANIFEST.length; i += 5) {
@@ -171,7 +174,10 @@ async function cleanupStaleAssets() {
 
   const cache = await caches.open(CACHE_NAME);
   const cachedRequests = await cache.keys();
-  const baseUrl = ASSET_ORIGIN || `${self.location.origin}${ASSET_PATH}`;
+  // Build base URL: CDN origin + asset path, or local origin + asset path
+  const baseUrl = ASSET_ORIGIN
+    ? `${ASSET_ORIGIN}${ASSET_PATH}`
+    : `${self.location.origin}${ASSET_PATH}`;
 
   // Build set of valid asset URLs from current manifest
   const validUrls = new Set(