diff --git a/moli-benchmark/moli_benchmark/wpt_cross/server.py b/moli-benchmark/moli_benchmark/wpt_cross/server.py
index bb22c9abff..02fb951e4b 100644
--- a/moli-benchmark/moli_benchmark/wpt_cross/server.py
+++ b/moli-benchmark/moli_benchmark/wpt_cross/server.py
@@ -1847,6 +1847,11 @@ def _wpt_cookie_websocket_set_cookie(query: str) -> str | None:
 
 
 class _FixtureThreadingHTTPServer(ThreadingHTTPServer):
+    # Match wptserve: parallel browsers open bursts of subresource connections.
+    # The stdlib backlog of five makes them wait for TCP retransmissions before
+    # their requests reach a handler, changing the timing the cases measure.
+    request_queue_size = 2000
+
     def handle_error(self, request: object, client_address: object) -> None:
         # Disposing a case BrowserContext intentionally cancels any auxiliary
         # requests that outlive the harness result. The stdlib server prints a
diff --git a/moli-benchmark/tests/test_wpt_connection_backlog.py b/moli-benchmark/tests/test_wpt_connection_backlog.py
new file mode 100644
index 0000000000..43a0441947
--- /dev/null
+++ b/moli-benchmark/tests/test_wpt_connection_backlog.py
@@ -0,0 +1,39 @@
+from __future__ import annotations
+
+import socket
+import unittest
+from contextlib import ExitStack, closing
+from http.server import BaseHTTPRequestHandler
+
+from moli_benchmark.wpt_cross.server import (
+    _FixtureThreadingHTTPServer,
+    _Ipv6ThreadingHTTPServer,
+)
+
+
+class FixtureConnectionBacklogTests(unittest.TestCase):
+    def assert_worker_burst_can_connect(
+        self,
+        server_class: type[_FixtureThreadingHTTPServer],
+        address: tuple[str, int],
+    ) -> None:
+        # Hold the accept loop so all connections coexist in the listen queue.
+        # This isolates queue capacity from handler speed and TCP retry timing.
+        with server_class(address, BaseHTTPRequestHandler) as server:
+            host, port = server.server_address[:2]
+            with ExitStack() as connections:
+                for _ in range(50):
+                    connections.enter_context(closing(socket.create_connection(
+                        (host, port), timeout=1,
+                    )))
+
+    def test_loopback_listener_accepts_a_full_worker_burst(self) -> None:
+        self.assert_worker_burst_can_connect(
+            _FixtureThreadingHTTPServer, ("127.0.0.1", 0),
+        )
+
+    @unittest.skipUnless(socket.has_ipv6, "IPv6 is unavailable")
+    def test_ipv6_listener_accepts_a_full_worker_burst(self) -> None:
+        self.assert_worker_burst_can_connect(
+            _Ipv6ThreadingHTTPServer, ("::1", 0),
+        )