diff --git a/src/core/observer/dep.js b/src/core/observer/dep.js
index 1dd37783490..0f7f0a60264 100644
--- a/src/core/observer/dep.js
+++ b/src/core/observer/dep.js
@@ -56,7 +56,7 @@ Dep.target = null
 const targetStack = []
 
 export function pushTarget (_target: ?Watcher) {
-  if (Dep.target) targetStack.push(Dep.target)
+  if (Dep.target !== null) targetStack.push(Dep.target)
   Dep.target = _target
 }