diff --git a/Libraries/LibWeb/HTML/PromiseRejectionEvent.h b/Libraries/LibWeb/HTML/PromiseRejectionEvent.h
index adc253b2d7f..e6a1d46d47e 100644
--- a/Libraries/LibWeb/HTML/PromiseRejectionEvent.h
+++ b/Libraries/LibWeb/HTML/PromiseRejectionEvent.h
@@ -17,7 +17,7 @@ namespace Web::HTML {
 
 struct PromiseRejectionEventInit : public DOM::EventInit {
     GC::Root<JS::Object> promise;
-    JS::Value reason;
+    JS::Value reason { JS::js_undefined() };
 };
 
 class PromiseRejectionEvent final : public DOM::Event {
diff --git a/Tests/LibWeb/Text/expected/wpt-import/html/webappapis/scripting/processing-model-2/unhandled-promise-rejections/promise-rejection-event-constructor.txt b/Tests/LibWeb/Text/expected/wpt-import/html/webappapis/scripting/processing-model-2/unhandled-promise-rejections/promise-rejection-event-constructor.txt
new file mode 100644
index 00000000000..a7be1022606
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/html/webappapis/scripting/processing-model-2/unhandled-promise-rejections/promise-rejection-event-constructor.txt
@@ -0,0 +1,11 @@
+Summary
+
+Harness status: OK
+
+Rerun
+
+Found 1 tests
+
+1 Pass
+Details
+Result	Test Name	MessagePass	This tests the constructor for the PromiseRejectionEvent DOM class.	
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/input/wpt-import/html/webappapis/scripting/processing-model-2/unhandled-promise-rejections/promise-rejection-event-constructor.html b/Tests/LibWeb/Text/input/wpt-import/html/webappapis/scripting/processing-model-2/unhandled-promise-rejections/promise-rejection-event-constructor.html
new file mode 100644
index 00000000000..50186871138
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/html/webappapis/scripting/processing-model-2/unhandled-promise-rejections/promise-rejection-event-constructor.html
@@ -0,0 +1,50 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<script src="../../../../../resources/testharness.js"></script>
+<script src="../../../../../resources/testharnessreport.js"></script>
+<link rel="help" href="https://html.spec.whatwg.org/#the-promiserejectionevent-interface">
+<script>
+'use strict';
+
+test(function() {
+  var p = new Promise(function(resolve, reject) {});
+
+  assert_throws_js(TypeError,
+                   function() {
+                     PromiseRejectionEvent('', { promise: p });
+                   },
+                   "Calling PromiseRejectionEvent constructor without 'new' must throw");
+
+  // No custom options are passed (besides required promise).
+  assert_equals(new PromiseRejectionEvent('eventType', { promise: p }).bubbles, false);
+  assert_equals(new PromiseRejectionEvent('eventType', { promise: p }).cancelable, false);
+  assert_equals(new PromiseRejectionEvent('eventType', { promise: p }).promise, p);
+  assert_equals(new PromiseRejectionEvent('eventType', { promise: p }).reason, undefined);
+
+  // No promise is passed.
+  assert_throws_js(TypeError,
+                   function() {
+                     new PromiseRejectionEvent('eventType', { bubbles: false });
+                   },
+                   'Cannot construct PromiseRejectionEventInit without promise');
+
+  // bubbles is passed.
+  assert_equals(new PromiseRejectionEvent('eventType', { bubbles: false, promise: p }).bubbles, false);
+  assert_equals(new PromiseRejectionEvent('eventType', { bubbles: true, promise: p }).bubbles, true);
+
+  // cancelable is passed.
+  assert_equals(new PromiseRejectionEvent('eventType', { cancelable: false, promise: p }).cancelable, false);
+  assert_equals(new PromiseRejectionEvent('eventType', { cancelable: true, promise: p }).cancelable, true);
+
+  // reason is passed.
+  var r = new Error();
+  assert_equals(new PromiseRejectionEvent('eventType', { promise: p, reason: r }).reason, r);
+  assert_equals(new PromiseRejectionEvent('eventType', { promise: p, reason: null }).reason, null);
+
+  // All initializers are passed.
+  assert_equals(new PromiseRejectionEvent('eventType', { bubbles: true, cancelable: true, promise: p, reason: r }).bubbles, true);
+  assert_equals(new PromiseRejectionEvent('eventType', { bubbles: true, cancelable: true, promise: p, reason: r }).cancelable, true);
+  assert_equals(new PromiseRejectionEvent('eventType', { bubbles: true, cancelable: true, promise: p, reason: r }).promise, p);
+  assert_equals(new PromiseRejectionEvent('eventType', { bubbles: true, cancelable: true, promise: p, reason: r }).reason, r);
+}, "This tests the constructor for the PromiseRejectionEvent DOM class.");
+</script>
