diff --git a/src/browser/tests/event/report_error.html b/src/browser/tests/event/report_error.html
new file mode 100644
index 00000000..353dc29e
--- /dev/null
+++ b/src/browser/tests/event/report_error.html
@@ -0,0 +1,38 @@
+<!DOCTYPE html>
+<script src="../testing.js"></script>
+
+<script id=onerrorFiveArguments>
+  let called = false;
+  let argCount = 0;
+  window.onerror = function() {
+    called = true;
+    argCount = arguments.length;
+    return true; // suppress default
+  };
+  try { undefinedVariable; } catch(e) { window.reportError(e); }
+  testing.expectEqual(true, called);
+  testing.expectEqual(5, argCount);
+  window.onerror = null;
+</script>
+
+<script id=onerrorCalledBeforeEventListener>
+  let callOrder = [];
+  window.onerror = function() { callOrder.push('onerror'); return true; };
+  window.addEventListener('error', function() { callOrder.push('listener'); });
+  try { undefinedVariable; } catch(e) { window.reportError(e); }
+  testing.expectEqual('onerror', callOrder[0]);
+  testing.expectEqual('listener', callOrder[1]);
+  window.onerror = null;
+</script>
+
+<script id=onerrorReturnTrueSuppresses>
+  let listenerCalled = false;
+  window.onerror = function() { return true; };
+  window.addEventListener('error', function(e) {
+    // listener still fires even when onerror returns true
+    listenerCalled = true;
+  });
+  try { undefinedVariable; } catch(e) { window.reportError(e); }
+  testing.expectEqual(true, listenerCalled);
+  window.onerror = null;
+</script>
diff --git a/src/browser/webapi/Window.zig b/src/browser/webapi/Window.zig
index 099cad65..1d12677c 100644
--- a/src/browser/webapi/Window.zig
+++ b/src/browser/webapi/Window.zig
@@ -343,7 +343,11 @@ pub fn reportError(self: *Window, err: js.Value, page: *Page) !void {
 
     const event = error_event.asEvent();
     event._prevent_default = prevent_default;
-    try page._event_manager.dispatch(self.asEventTarget(), event);
+    // Pass null as handler: onerror was already called above with 5 args.
+    // We still dispatch so that addEventListener('error', ...) listeners fire.
+    try page._event_manager.dispatchDirect(self.asEventTarget(), event, null, .{
+        .context = "window.reportError",
+    });
 
     if (comptime builtin.is_test == false) {
         if (!event._prevent_default) {
@@ -874,3 +878,7 @@ test "WebApi: Window" {
 test "WebApi: Window scroll" {
     try testing.htmlRunner("window_scroll.html", .{});
 }
+
+test "WebApi: Window.onerror" {
+    try testing.htmlRunner("event/report_error.html", .{});
+}
