diff --git a/asyncforge.js b/asyncforge.js
index 2ac45a4..00881f4 100644
--- a/asyncforge.js
+++ b/asyncforge.js
@@ -36,7 +36,10 @@ function memo (name) {
 
   function get () {
     const store = asyncLocalStorage.getStore()
-    return store?.[sym]
+    if (!store) {
+      throw new Error('asyncforge store is not initialized')
+    }
+    return store[sym]
   }
 
   function set (value) {
diff --git a/test/do-not-start-memo.test.js b/test/do-not-start-memo.test.js
index 13e6c52..0bd6307 100644
--- a/test/do-not-start-memo.test.js
+++ b/test/do-not-start-memo.test.js
@@ -8,7 +8,7 @@ test('memo without start', async (t) => {
   const p = tspl(t, { plan: 6 })
   const a = memo()
 
-  p.deepStrictEqual(a(), undefined)
+  p.throws(() => a())
   a.set({ value: 'bar' })
   p.deepStrictEqual(a(), { value: 'bar' })
 
@@ -42,7 +42,7 @@ test('nested', async (t) => {
   const p = tspl(t, { plan: 5 })
   const a = memo()
 
-  p.deepStrictEqual(a(), undefined)
+  p.throws(() => a())
   a.set({ value: 'bar' })
   p.deepStrictEqual(a(), { value: 'bar' })