diff --git a/src/diff/props.js b/src/diff/props.js
index 31bbb5daf5..8ef0e273cf 100644
--- a/src/diff/props.js
+++ b/src/diff/props.js
@@ -1,6 +1,17 @@
 import { IS_NON_DIMENSIONAL, NULL, SVG_NAMESPACE } from '../constants';
 import options from '../options';
 
+// Per-instance unique key for event clock stamps. Each Preact copy on the page
+// gets its own random suffix so that `_dispatched` / `_attached` properties on
+// shared event objects and handler functions cannot collide across instances.
+// ~1 in 60M collision odds - if you have that many praect versions on the page,
+// you deserve some weird bugs.
+// In 11 we can replace this with a
+// Symbol
+let _id = Math.random().toString(8),
+	EVENT_DISPATCHED = '__d' + _id,
+	EVENT_ATTACHED = '__a' + _id;
+
 function setStyle(style, key, value) {
 	if (key[0] == '-') {
 		style.setProperty(key, value == NULL ? '' : value);
@@ -79,14 +90,14 @@ export function setProperty(dom, name, value, oldValue, namespace) {
 
 		if (value) {
 			if (!oldValue) {
-				value._attached = eventClock;
+				value[EVENT_ATTACHED] = eventClock;
 				dom.addEventListener(
 					name,
 					useCapture ? eventProxyCapture : eventProxy,
 					useCapture
 				);
 			} else {
-				value._attached = oldValue._attached;
+				value[EVENT_ATTACHED] = oldValue[EVENT_ATTACHED];
 			}
 		} else {
 			dom.removeEventListener(
@@ -155,13 +166,13 @@ function createEventProxy(useCapture) {
 	return function (e) {
 		if (this._listeners) {
 			const eventHandler = this._listeners[e.type + useCapture];
-			if (e._dispatched == NULL) {
-				e._dispatched = eventClock++;
+			if (e[EVENT_DISPATCHED] == NULL) {
+				e[EVENT_DISPATCHED] = eventClock++;
 
-				// When `e._dispatched` is smaller than the time when the targeted event
+				// When `e[EVENT_DISPATCHED]` is smaller than the time when the targeted event
 				// handler was attached we know we have bubbled up to an element that was added
 				// during patching the DOM.
-			} else if (e._dispatched < eventHandler._attached) {
+			} else if (e[EVENT_DISPATCHED] < eventHandler[EVENT_ATTACHED]) {
 				return;
 			}
 			return eventHandler(options.event ? options.event(e) : e);
diff --git a/src/internal.d.ts b/src/internal.d.ts
index 481d4b12d8..58e0d54d62 100644
--- a/src/internal.d.ts
+++ b/src/internal.d.ts
@@ -125,7 +125,9 @@ export interface PreactElement extends preact.ContainerNode {
 }
 
 export interface PreactEvent extends Event {
-	_dispatched?: number;
+	// Keyed by a per-instance unique string (e.g. `__dXXXXX`) so that
+	// multiple Preact copies on the same page don't share event clock stamps.
+	[key: string]: any;
 }
 
 // We use the `current` property to differentiate between the two kinds of Refs so