diff --git a/src/__tests__/events.js b/src/__tests__/events.js
index 5ff0118d..b79cea35 100644
--- a/src/__tests__/events.js
+++ b/src/__tests__/events.js
@@ -383,6 +383,8 @@ test('assigns read-only target properties', () => {
 
   expect(node.scrollWidth).toBe(0)
   fireEvent.scroll(node, {target: {scrollWidth: 10}})
+
+  expect(spy).toHaveBeenCalledTimes(1)
   expect(node.scrollWidth).toBe(10)
 })
 
diff --git a/src/events.js b/src/events.js
index 1fb960dc..aba4f7b4 100644
--- a/src/events.js
+++ b/src/events.js
@@ -46,14 +46,13 @@ function createEvent(
     })
   }
 
-  const modifiableProperties = {}
+  // Make read-only properties of events specifiable for tests.
   Object.keys(targetProperties).forEach(key => {
-    modifiableProperties[key] = {
+    Object.defineProperty(node, key, {
       value: targetProperties[key],
       writable: true,
-    }
+    })
   })
-  Object.defineProperties(node, modifiableProperties)
 
   const window = getWindowFromNode(node)
   const EventConstructor = window[EventType] || window.Event