--- a/testing/web-platform/tests/webdriver/tests/element_retrieval/get_active_element.py
+++ b/testing/web-platform/tests/webdriver/tests/element_retrieval/get_active_element.py
@@ -10,16 +10,17 @@ def get_active_element(session):
 def assert_is_active_element(session, response):
     """Ensure that the provided object is a successful WebDriver
     response describing an element reference and that the referenced
     element matches the element returned by the `activeElement`
     attribute of the current browsing context's active document.
 
     """
     assert response.status == 200
+    assert "value" in response.body
 
     from_js = session.execute_script("return document.activeElement")
 
     if response.body["value"] is None:
         assert from_js is None
     else:
         assert_same_element(session, response.body["value"], from_js)