diff --git a/packages/reactivity/__tests__/effect.spec.ts b/packages/reactivity/__tests__/effect.spec.ts
index 69d24a76520..635e6534abe 100644
--- a/packages/reactivity/__tests__/effect.spec.ts
+++ b/packages/reactivity/__tests__/effect.spec.ts
@@ -585,6 +585,14 @@ describe('reactivity/effect', () => {
     expect(runner.effect.fn).toBe(otherRunner.effect.fn)
   })
 
+  it('should wrap if the passed function is a fake effect', () => {
+    const fakeRunner = () => {}
+    fakeRunner.effect = {}
+    const runner = effect(fakeRunner)
+    expect(fakeRunner).not.toBe(runner)
+    expect(runner.effect.fn).toBe(fakeRunner)
+  })
+
   it('should not run multiple times for a single mutation', () => {
     let dummy
     const obj = reactive<Record<string, number>>({})
diff --git a/packages/reactivity/src/effect.ts b/packages/reactivity/src/effect.ts
index d4a34edfef4..bbac96a4b2a 100644
--- a/packages/reactivity/src/effect.ts
+++ b/packages/reactivity/src/effect.ts
@@ -16,7 +16,7 @@ import { ComputedRefImpl } from './computed'
 // which maintains a Set of subscribers, but we simply store them as
 // raw Sets to reduce memory overhead.
 type KeyToDepMap = Map<any, Dep>
-const targetMap = new WeakMap<any, KeyToDepMap>()
+const targetMap = new WeakMap<object, KeyToDepMap>()
 
 // The number of effects currently being tracked recursively.
 let effectTrackDepth = 0
@@ -181,7 +181,7 @@ export function effect<T = any>(
   fn: () => T,
   options?: ReactiveEffectOptions
 ): ReactiveEffectRunner {
-  if ((fn as ReactiveEffectRunner).effect) {
+  if ((fn as ReactiveEffectRunner).effect instanceof ReactiveEffect) {
     fn = (fn as ReactiveEffectRunner).effect.fn
   }