1 files changed, 2 insertions, 1 deletions
diff --git a/testing/web-platform/tests/navigation-api/navigate-event/navigate-history-back-cross-document.html b/testing/web-platform/tests/navigation-api/navigate-event/navigate-history-back-cross-document.html
index 29c626a522..a34b20a5e5 100644
--- a/testing/web-platform/tests/navigation-api/navigate-event/navigate-history-back-cross-document.html
+++ b/testing/web-platform/tests/navigation-api/navigate-event/navigate-history-back-cross-document.html
@@ -23,7 +23,8 @@ async_test(t => {
         assert_equals(e.destination.index, 0);
         assert_equals(e.formData, null);
         assert_equals(e.info, undefined);
-        assert_equals(e.sourceElement, null);
+        // NavigateEvent sourceElement is still in development, so test whether it is available.
+        if ("sourceElement" in e) assert_equals(e.sourceElement, null);
       });
       assert_true(i.contentWindow.navigation.canGoBack);
       i.contentWindow.history.back();