diff --git a/.changeset/idb-storage-memory-fallback.md b/.changeset/idb-storage-memory-fallback.md
new file mode 100644
index 00000000..0499203d
--- /dev/null
+++ b/.changeset/idb-storage-memory-fallback.md
@@ -0,0 +1,5 @@
+---
+'accounts': patch
+---
+
+Fell back to in-memory storage in `Storage.idb()` when IndexedDB is unavailable (e.g. React Native/Expo, some SSR), instead of throwing `ReferenceError: indexedDB is not defined` on the first read or write.
diff --git a/src/core/Storage.test.ts b/src/core/Storage.test.ts
new file mode 100644
index 00000000..0d23532d
--- /dev/null
+++ b/src/core/Storage.test.ts
@@ -0,0 +1,24 @@
+import { expect, test } from 'vp/test'
+
+import * as Storage from './Storage.js'
+
+// In runtimes that expose `window` but not IndexedDB (React Native/Expo, some
+// SSR), `idb()` is still selected as the default storage. It must degrade to a
+// working in-memory adapter instead of throwing: idb-keyval treats an
+// `undefined` store as "use the default store", which opens IndexedDB and
+// throws `ReferenceError: indexedDB is not defined`.
+test('idb: degrades to in-memory storage when IndexedDB is unavailable', async () => {
+  expect(typeof indexedDB).toBe('undefined')
+
+  const storage = Storage.idb()
+
+  await storage.setItem('accounts', ['0xabc'])
+  expect(await storage.getItem('accounts')).toMatchInlineSnapshot(`
+    [
+      "0xabc",
+    ]
+  `)
+
+  await storage.removeItem('accounts')
+  expect(await storage.getItem('accounts')).toMatchInlineSnapshot(`null`)
+})
diff --git a/src/core/Storage.ts b/src/core/Storage.ts
index dea85524..95cf7378 100644
--- a/src/core/Storage.ts
+++ b/src/core/Storage.ts
@@ -156,9 +156,13 @@ export declare namespace cookie {
   type Options = from.Options
 }
 
-/** Creates an IndexedDB-backed storage adapter. Stores raw values (no JSON serialization). */
+/** Creates an IndexedDB-backed storage adapter. Stores raw values (no JSON serialization). Falls back to in-memory storage in runtimes without IndexedDB (e.g. React Native, some SSR). */
 export function idb(options: idb.Options = {}): Storage {
-  const store = typeof indexedDB !== 'undefined' ? createStore('tempo', 'store') : undefined
+  // idb-keyval treats an `undefined` store as "use the default store", which
+  // opens IndexedDB and throws where it is unavailable — so degrade to memory
+  // rather than passing `undefined` through.
+  if (typeof indexedDB === 'undefined') return memory(options)
+  const store = createStore('tempo', 'store')
   const storage = from(
     {
       async getItem(name) {