diff --git a/tests/core/test_vault_bad_keys.py b/tests/core/test_vault_bad_keys.py
index 8274351e..1ff8df96 100644
--- a/tests/core/test_vault_bad_keys.py
+++ b/tests/core/test_vault_bad_keys.py
@@ -232,14 +232,17 @@ def test_retry_takes_the_next_parallel_answer_without_a_new_request(tmp_path: Pa
     from tests.core.test_vaults_lookup import FakeVault
 
     local = SQLite("local", tmp_path / "local.db")
-    fast = FakeVault("fast", BAD, delay=0.01)
-    slow = FakeVault("slow", GOOD, delay=0.2)
+    # the fast answer must land after the slow query has started, or the pool shutdown cancels
+    # the slow query before it runs and it never reaches candidates; a loaded CI runner can take
+    # tens of milliseconds to start the second worker thread
+    fast = FakeVault("fast", BAD, delay=0.1)
+    slow = FakeVault("slow", GOOD, delay=0.3)
     vaults = Vaults("SVC")
     vaults.vaults = [local, fast, slow]
 
     assert vaults.get_key(KID) == (BAD, fast)
     vaults.flag_bad_key(KID, BAD)
-    time.sleep(0.4)  # the slow answer lands in candidates after the first call returned
+    time.sleep(0.5)  # the slow answer lands in candidates after the first call returned
     assert vaults.get_key(KID) == (GOOD, slow)
     assert fast.calls == 1 and slow.calls == 1