diff --git a/tests/setup.ts b/tests/setup.ts
new file mode 100644
index 0000000..51d385c
--- /dev/null
+++ b/tests/setup.ts
@@ -0,0 +1,15 @@
+// Node 26 ships its own `localStorage` global, undefined unless the process gets
+// --localstorage-file, and it shadows the one jsdom installs. Modules that read
+// storage at import time then throw before a single test runs.
+if (!globalThis.localStorage) {
+  const store = new Map<string, string>();
+  const shim: Storage = {
+    get length() { return store.size; },
+    key: (i) => [...store.keys()][i] ?? null,
+    getItem: (k) => store.get(k) ?? null,
+    setItem: (k, v) => void store.set(k, String(v)),
+    removeItem: (k) => void store.delete(k),
+    clear: () => store.clear(),
+  };
+  Object.defineProperty(globalThis, 'localStorage', { value: shim, configurable: true });
+}
diff --git a/vite.config.ts b/vite.config.ts
index 584d000..8dc70c7 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -19,6 +19,7 @@ export default defineConfig({
   // jsdom supplies a global DOMParser, so the export/import specs need no setup.
   test: {
     environment: 'jsdom',
+    setupFiles: ['tests/setup.ts'],
     include: ['tests/**/*.test.ts'],
     globals: false,
     // A build+re-import leg runs ~10s when the whole suite competes for the CPU,