diff --git a/lib/common/utils.ts b/lib/common/utils.ts
index 2d292bf4f..c183fe5a6 100644
--- a/lib/common/utils.ts
+++ b/lib/common/utils.ts
@@ -21,6 +21,7 @@ const _global: any =
 const FUNCTION = 'function';
 const UNDEFINED = 'undefined';
 const REMOVE_ATTRIBUTE = 'removeAttribute';
+const NULL_ON_PROP_VALUE: any[] = [null];
 
 export function bindArguments(args: any[], source: string): any[] {
   for (let i = args.length - 1; i >= 0; i--) {
@@ -141,6 +142,7 @@ export function patchProperty(obj: any, prop: string, prototype?: any) {
   delete desc.writable;
   delete desc.value;
   const originalDescGet = desc.get;
+  const originalDescSet = desc.set;
 
   // substr(2) cuz 'onclick' -> 'click', etc
   const eventName = prop.substr(2);
@@ -165,6 +167,12 @@ export function patchProperty(obj: any, prop: string, prototype?: any) {
       target.removeEventListener(eventName, wrapFn);
     }
 
+    // issue #978, when onload handler was added before loading zone.js
+    // we should remove it with originalDescSet
+    if (originalDescSet) {
+      originalDescSet.apply(target, NULL_ON_PROP_VALUE);
+    }
+
     if (typeof newValue === 'function') {
       target[eventNameSymbol] = newValue;
       target.addEventListener(eventName, wrapFn, false);
diff --git a/test/browser/browser.spec.ts b/test/browser/browser.spec.ts
index b59337542..5365aeb21 100644
--- a/test/browser/browser.spec.ts
+++ b/test/browser/browser.spec.ts
@@ -225,6 +225,29 @@ describe('Zone', function() {
             });
           });
 
+          it('should be able to clear on handler added before load zone.js', function() {
+            const TestTarget: any = (window as any)['TestTarget'];
+            patchFilteredProperties(
+                TestTarget.prototype, ['prop3'], global['__Zone_ignore_on_properties']);
+            const testTarget = new TestTarget();
+            Zone.current.fork({name: 'test'}).run(() => {
+              expect(testTarget.onprop3).toBeTruthy();
+              const newProp3Handler = function() {};
+              testTarget.onprop3 = newProp3Handler;
+              expect(testTarget.onprop3).toBe(newProp3Handler);
+              testTarget.onprop3 = null;
+              expect(!testTarget.onprop3).toBeTruthy();
+              testTarget.onprop3 = function() {
+                // onprop1 should not be patched
+                expect(Zone.current.name).toEqual('test');
+              };
+            });
+
+            Zone.current.fork({name: 'test1'}).run(() => {
+              testTarget.dispatchEvent('prop3');
+            });
+          });
+
           it('window onclick should be in zone',
              ifEnvSupports(canPatchOnProperty(window, 'onmousedown'), function() {
                zone.run(function() {
diff --git a/test/test_fake_polyfill.ts b/test/test_fake_polyfill.ts
index 75be59dce..e5e92c4f0 100644
--- a/test/test_fake_polyfill.ts
+++ b/test/test_fake_polyfill.ts
@@ -32,6 +32,16 @@
   Object.defineProperties(TestTarget.prototype, {
     'onprop1': {configurable: true, writable: true},
     'onprop2': {configurable: true, writable: true},
+    'onprop3': {
+      configurable: true,
+      get: function() {
+        return this._onprop3;
+      },
+      set: function(_value) {
+        this._onprop3 = _value;
+      }
+    },
+    '_onprop3': {configurable: true, writable: true, value: function() {}},
     'addEventListener': {
       configurable: true,
       writable: true,