diff --git a/tests/cron/test_cron_script.py b/tests/cron/test_cron_script.py
index 783320728bd..ee02d043017 100644
--- a/tests/cron/test_cron_script.py
+++ b/tests/cron/test_cron_script.py
@@ -137,7 +137,9 @@ class TestRunJobScript:
         from tools.environments.local import _HERMES_PROVIDER_ENV_BLOCKLIST
         from cron.scheduler import _run_job_script
 
-        blocked_var = next(iter(_HERMES_PROVIDER_ENV_BLOCKLIST))
+        # sorted() so the probed var is deterministic across runs
+        # (frozenset iteration order varies with PYTHONHASHSEED).
+        blocked_var = sorted(_HERMES_PROVIDER_ENV_BLOCKLIST)[0]
         monkeypatch.setenv(blocked_var, "must_not_leak")
 
         script = cron_env / "scripts" / "env_probe.py"