diff --git a/src/mount.ts b/src/mount.ts
index f19a40923..dfb9d974f 100644
--- a/src/mount.ts
+++ b/src/mount.ts
@@ -237,6 +237,11 @@ export function mount(
     isLegacyFunctionalComponent(originalComponent)
   ) {
     component = defineComponent({
+      compatConfig: {
+        MODE: 3,
+        INSTANCE_LISTENERS: false,
+        INSTANCE_ATTRS_CLASS_STYLE: false
+      },
       setup:
         (_, { attrs, slots }) =>
         () =>
diff --git a/src/utils/vueCompatSupport.ts b/src/utils/vueCompatSupport.ts
index 8334b6b3d..ea17229f6 100644
--- a/src/utils/vueCompatSupport.ts
+++ b/src/utils/vueCompatSupport.ts
@@ -32,10 +32,10 @@ export function isLegacyFunctionalComponent(component: unknown) {
     return false
   }
 
-  return (
+  return Boolean(
     component &&
-    typeof component === 'object' &&
-    hasOwnProperty(component, 'functional') &&
-    component.functional
+      typeof component === 'object' &&
+      hasOwnProperty(component, 'functional') &&
+      component.functional
   )
 }
diff --git a/tests-compat/compat.spec.ts b/tests-compat/compat.spec.ts
index f922602c0..cc0ac085b 100644
--- a/tests-compat/compat.spec.ts
+++ b/tests-compat/compat.spec.ts
@@ -143,4 +143,35 @@ describe('@vue/compat build', () => {
 
     expect(wrapper.vm.foo).toBe('bar')
   })
+
+  it('correctly passes all props to functional component', async () => {
+    configureCompat({
+      MODE: 3,
+      INSTANCE_LISTENERS: 'suppress-warning',
+      INSTANCE_ATTRS_CLASS_STYLE: 'suppress-warning'
+    })
+
+    const FunctionalComponent = {
+      functional: true,
+      render(h: any, context: any) {
+        return h('div', context.data, context.props.text)
+      }
+    }
+
+    const onClick = jest.fn()
+    const wrapper = mount(FunctionalComponent, {
+      props: {
+        class: 'foo',
+        text: 'message',
+        style: { color: 'red' },
+        onClick
+      }
+    })
+    expect(wrapper.text()).toBe('message')
+    await wrapper.trigger('click')
+    expect(onClick).toHaveBeenCalled()
+    expect(wrapper.html()).toBe(
+      '<div class="foo" text="message" style="color: red;">message</div>'
+    )
+  })
 })