diff --git a/lib/utils.js b/lib/utils.js
index 85297cb..5e8ad58 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -1,10 +1,22 @@
 // @ts-check
-/** @typedef {{ promise: Promise<void>, resolve: (value: void | PromiseLike<void>) => void, reject: (reason?: any) => void }} DeferredPromise */
+
+/**
+ * @internal
+ * @template [T=void]
+ * @typedef {object} DeferredPromise
+ * @prop {Promise<T>} promise
+ * @prop {(value: T | PromiseLike<T>) => void} resolve
+ * @prop {(reason: unknown) => void} reject
+ */
+
+/**
+ * @template [T=void]
+ * @returns {DeferredPromise<T>}
+ */
 function pDefer() {
-  /** @type {DeferredPromise} */
+  /** @type {DeferredPromise<T>} */
   const deferred = {}
-
-  /** @type {Promise<void>} */
+  /** @type {Promise<T>} */
   deferred.promise = new Promise((res, rej) => {
     deferred.resolve = res
     deferred.reject = rej
diff --git a/test/multi-core-indexer.test.js b/test/multi-core-indexer.test.js
index 728083d..fad72f5 100644
--- a/test/multi-core-indexer.test.js
+++ b/test/multi-core-indexer.test.js
@@ -2,6 +2,7 @@
 const MultiCoreIndexer = require('../')
 const test = require('node:test')
 const assert = require('node:assert/strict')
+const { setTimeout: delay } = require('node:timers/promises')
 const ram = require('random-access-memory')
 const {
   create,
@@ -11,10 +12,42 @@ const {
   sortEntries,
 } = require('./helpers')
 const { testKeypairs, expectedStorageNames } = require('./fixtures.js')
+const { pDefer } = require('../lib/utils.js')
 const Hypercore = require('hypercore')
 
 /** @typedef {import('../lib/types').Entry<'binary'>} Entry */
 
+test('Indexer waits for core to be ready before idling', async (t) => {
+  const delayingCoreReady = pDefer()
+  t.after(() => delayingCoreReady.resolve({}))
+
+  const core = new Hypercore(ram, {
+    preload: () => delayingCoreReady.promise,
+  })
+  assert(!isCoreReady(core), 'test setup: core is not ready at the start')
+
+  const indexer = new MultiCoreIndexer([core], {
+    batch: async () => {
+      assert.fail('This should never be called')
+    },
+    storage: () => new ram(),
+  })
+  t.after(() => indexer.close())
+
+  assert(!isCoreReady(core), 'test setup: core is still not ready')
+  assert.equal(indexer.state.current, 'indexing')
+
+  await delay(1)
+
+  assert(!isCoreReady(core), 'test setup: core is still not ready')
+  assert.equal(indexer.state.current, 'indexing')
+
+  delayingCoreReady.resolve({})
+
+  await indexer.idle()
+  assert.equal(indexer.state.current, 'idle')
+})
+
 test('Indexes all items already in a core', async () => {
   const cores = await createMultiple(5)
   const expected = await generateFixtures(cores, 100)
@@ -687,3 +720,11 @@ test('Indexes all items already in a core - cores not ready', async () => {
   assert.deepEqual(sortEntries(entries), sortEntries(expected))
   await indexer.close()
 })
+
+/**
+ * @param {Readonly<Hypercore>} core
+ * @returns {boolean}
+ */
+function isCoreReady(core) {
+  return core.writable
+}