diff --git a/packages/runtime-core/__tests__/apiWatch.spec.ts b/packages/runtime-core/__tests__/apiWatch.spec.ts
index c9db3657367..8f5ce474c55 100644
--- a/packages/runtime-core/__tests__/apiWatch.spec.ts
+++ b/packages/runtime-core/__tests__/apiWatch.spec.ts
@@ -186,7 +186,7 @@ describe('api: watch', () => {
       (newVal, oldVal) => {
         called = true
         expect(newVal).toMatchObject([undefined, undefined])
-        expect(oldVal).toBeUndefined()
+        expect(oldVal).toMatchObject([undefined, undefined])
       },
       { immediate: true }
     )
diff --git a/packages/runtime-core/src/apiWatch.ts b/packages/runtime-core/src/apiWatch.ts
index 180843cf745..d047767f4c4 100644
--- a/packages/runtime-core/src/apiWatch.ts
+++ b/packages/runtime-core/src/apiWatch.ts
@@ -335,7 +335,9 @@ function doWatch(
           // pass undefined as the old value when it's changed for the first time
           oldValue === INITIAL_WATCHER_VALUE ||
           (isMultiSource && oldValue[0] === INITIAL_WATCHER_VALUE)
-            ? undefined
+            ? isMultiSource
+              ? new Array((source as []).length).fill(undefined)
+              : undefined
             : oldValue,
           onCleanup
         ])