diff --git a/vitest.config.ts b/vitest.config.ts
new file mode 100644
index 0000000..f744c57
--- /dev/null
+++ b/vitest.config.ts
@@ -0,0 +1,16 @@
+import { defineConfig } from "vitest/config";
+
+const nodeMajor = Number(process.versions.node.split(".")[0]);
+
+// Node 25+ ships Web Storage on globalThis by default. The built-in localStorage
+// is incomplete without --localstorage-file, so jsdom skips its polyfill and tests
+// that call localStorage.clear() fail. --no-webstorage disables Node's API so jsdom
+// can provide a full Storage implementation.
+// On Node < 25 the flag does not exist (CI uses Node 20), so we must omit it there.
+const modernNodeExecArgv = nodeMajor >= 25 ? ["--no-webstorage"] : [];
+
+export default defineConfig({
+  test: {
+    execArgv: modernNodeExecArgv,
+  },
+});