diff --git a/vite.config.ts b/vite.config.ts
index e6dfbe2..21e2681 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -31,5 +31,11 @@ export default defineConfig({
   test: {
     environment: 'happy-dom',
     include: ['tests/**/*.test.ts'],
+    // Tests never reach the network: happy-dom must not load the pages of
+    // iframes (the preview frame's srcdoc holds test payloads with remote
+    // URLs).
+    environmentOptions: {
+      happyDOM: { settings: { disableIframePageLoading: true } },
+    },
   },
 })