diff --git a/test/fixtures/wpt/xhr/request-content-length.any.js b/test/fixtures/wpt/xhr/request-content-length.any.js
index 054d2cce9d2..69a1e168365 100644
--- a/test/fixtures/wpt/xhr/request-content-length.any.js
+++ b/test/fixtures/wpt/xhr/request-content-length.any.js
@@ -11,6 +11,7 @@ async_test(test => {
     assert_true(happened);
     assert_true(client.responseText.includes(`Content-Length: ${data.length}`));
   });
+  client.onerror = test.unreached_func();
   client.open("POST", "resources/echo-headers.py");
   client.send(data);
 }, "Uploads need to set the Content-Length header");
diff --git a/test/fixtures/wpt/xhr/resources/echo-headers.py b/test/fixtures/wpt/xhr/resources/echo-headers.py
index 58a7ed5637f..63943082b63 100644
--- a/test/fixtures/wpt/xhr/resources/echo-headers.py
+++ b/test/fixtures/wpt/xhr/resources/echo-headers.py
@@ -1,7 +1,9 @@
 def main(request, response):
+    content = str(request.raw_headers)
     response.writer.write_status(200)
     response.writer.write_header(b"Content-Type", b"text/plain")
+    response.writer.write_header(b"Content-Length", str(len(content)))
     response.writer.write_header(b"Connection", b"close")
     response.writer.end_headers()
-    response.writer.write(str(request.raw_headers))
+    response.writer.write(content)
     response.close_connection = True