diff --git a/packages/zone.js/lib/browser/event-target.ts b/packages/zone.js/lib/browser/event-target.ts
index 412eb4964d4d..3439d1388592 100644
--- a/packages/zone.js/lib/browser/event-target.ts
+++ b/packages/zone.js/lib/browser/event-target.ts
@@ -7,7 +7,8 @@
  */
 
 export function eventTargetPatch(_global: any, api: _ZonePrivate) {
-  if ((Zone as any)[api.symbol('patchEventTarget')]) {
+  const patchSym = api.symbol('patchEventTarget');
+  if ((Zone as any).hasOwnProperty(patchSym) && (Zone as any)[patchSym]) {
     // EventTarget is already patched.
     return;
   }
diff --git a/packages/zone.js/lib/common/events.ts b/packages/zone.js/lib/common/events.ts
index 73a67cfd2c8c..f64642677601 100644
--- a/packages/zone.js/lib/common/events.ts
+++ b/packages/zone.js/lib/common/events.ts
@@ -488,7 +488,11 @@ export function patchEventTarget(
 
     const compare = patchOptions?.diff || compareTaskCallbackVsDelegate;
 
-    const unpatchedEvents: string[] = (Zone as any)[zoneSymbol('UNPATCHED_EVENTS')];
+    const unpatchedSymbol = zoneSymbol('UNPATCHED_EVENTS');
+    const unpatchedEvents: string[] = (Zone as any).hasOwnProperty(unpatchedSymbol)
+      ? (Zone as any)[unpatchedSymbol]
+      : [];
+
     const passiveEvents: string[] = _global[zoneSymbol('PASSIVE_EVENTS')];
 
     function copyEventListenerOptions(options: any) {