diff --git a/src/mount.ts b/src/mount.ts
index 04d78c868..917489fbe 100644
--- a/src/mount.ts
+++ b/src/mount.ts
@@ -100,13 +100,26 @@ export function mount(
     }
 
     to.appendChild(el)
-    app.onUnmount(() => {
+    const removeContainer = () => {
       // The wrapper may already have been manually unmounted before auto-unmount
       // runs, so the container can already be removed from its parent.
       if (el.parentNode === to) {
         to.removeChild(el)
       }
-    })
+    }
+    if (app.onUnmount) {
+      app.onUnmount(removeContainer)
+    } else {
+      // app.onUnmount is only available since Vue 3.5
+      const unmount = app.unmount
+      app.unmount = () => {
+        try {
+          unmount()
+        } finally {
+          removeContainer()
+        }
+      }
+    }
   }
   const vm = app.mount(el)
   if (errorsOnMount.length) {
diff --git a/tests/mount.spec.ts b/tests/mount.spec.ts
index 534771003..619c68908 100644
--- a/tests/mount.spec.ts
+++ b/tests/mount.spec.ts
@@ -118,4 +118,25 @@ describe('mount: general tests', () => {
     wrapper.unmount()
     expect(document.body.firstChild, 'Container should be empty').toBeNull()
   })
+
+  // app.onUnmount only exists since Vue 3.5
+  it('supports attachTo without app.onUnmount', () => {
+    const wrapper = mount(Hello, {
+      props: { msg: 'Hello world' },
+      attachTo: document.body,
+      global: {
+        plugins: [
+          {
+            install(app: any) {
+              app.onUnmount = undefined
+            }
+          }
+        ]
+      }
+    })
+    expect(document.body.firstChild).toBeInstanceOf(HTMLDivElement)
+
+    wrapper.unmount()
+    expect(document.body.firstChild).toBeNull()
+  })
 })