diff --git a/cron/scheduler.py b/cron/scheduler.py
index 685b8ae560..941aff3a3e 100644
--- a/cron/scheduler.py
+++ b/cron/scheduler.py
@@ -1053,7 +1053,18 @@ def run_job(job: dict) -> tuple[bool, str, str, Optional[str]]:
         #
         # Uses the agent's built-in activity tracker (updated by
         # _touch_activity() on every tool call, API call, and stream delta).
-        _cron_timeout = float(os.getenv("HERMES_CRON_TIMEOUT", 600))
+        _raw_cron_timeout = os.getenv("HERMES_CRON_TIMEOUT", "").strip()
+        if _raw_cron_timeout:
+            try:
+                _cron_timeout = float(_raw_cron_timeout)
+            except (ValueError, TypeError):
+                logger.warning(
+                    "Invalid HERMES_CRON_TIMEOUT=%r; using default 600s",
+                    _raw_cron_timeout,
+                )
+                _cron_timeout = 600.0
+        else:
+            _cron_timeout = 600.0
         _cron_inactivity_limit = _cron_timeout if _cron_timeout > 0 else None
         _POLL_INTERVAL = 5.0
         _cron_pool = concurrent.futures.ThreadPoolExecutor(max_workers=1)
diff --git a/tests/cron/test_cron_inactivity_timeout.py b/tests/cron/test_cron_inactivity_timeout.py
index 0b83f64f07..67e932089f 100644
--- a/tests/cron/test_cron_inactivity_timeout.py
+++ b/tests/cron/test_cron_inactivity_timeout.py
@@ -169,10 +169,20 @@ class TestInactivityTimeout:
 
         assert result["final_response"] == "Done"
 
+    def _parse_cron_timeout(self, raw_value):
+        """Mirror the defensive parsing logic from cron/scheduler.py run_job()."""
+        if raw_value:
+            try:
+                return float(raw_value)
+            except (ValueError, TypeError):
+                return 600.0
+        return 600.0
+
     def test_timeout_env_var_parsing(self, monkeypatch):
         """HERMES_CRON_TIMEOUT env var is respected."""
         monkeypatch.setenv("HERMES_CRON_TIMEOUT", "1200")
-        _cron_timeout = float(os.getenv("HERMES_CRON_TIMEOUT", 600))
+        raw = os.getenv("HERMES_CRON_TIMEOUT", "").strip()
+        _cron_timeout = self._parse_cron_timeout(raw)
         assert _cron_timeout == 1200.0
 
         _cron_inactivity_limit = _cron_timeout if _cron_timeout > 0 else None
@@ -181,10 +191,27 @@ class TestInactivityTimeout:
     def test_timeout_zero_means_unlimited(self, monkeypatch):
         """HERMES_CRON_TIMEOUT=0 yields None (unlimited)."""
         monkeypatch.setenv("HERMES_CRON_TIMEOUT", "0")
-        _cron_timeout = float(os.getenv("HERMES_CRON_TIMEOUT", 600))
+        raw = os.getenv("HERMES_CRON_TIMEOUT", "").strip()
+        _cron_timeout = self._parse_cron_timeout(raw)
         _cron_inactivity_limit = _cron_timeout if _cron_timeout > 0 else None
         assert _cron_inactivity_limit is None
 
+    def test_timeout_invalid_value_falls_back_to_default(self, monkeypatch):
+        """HERMES_CRON_TIMEOUT=abc should fall back to 600s, not raise ValueError."""
+        monkeypatch.setenv("HERMES_CRON_TIMEOUT", "abc")
+        raw = os.getenv("HERMES_CRON_TIMEOUT", "").strip()
+        _cron_timeout = self._parse_cron_timeout(raw)
+        assert _cron_timeout == 600.0
+        _cron_inactivity_limit = _cron_timeout if _cron_timeout > 0 else None
+        assert _cron_inactivity_limit == 600.0
+
+    def test_timeout_empty_string_uses_default(self, monkeypatch):
+        """HERMES_CRON_TIMEOUT='' (empty) should use the 600s default."""
+        monkeypatch.setenv("HERMES_CRON_TIMEOUT", "")
+        raw = os.getenv("HERMES_CRON_TIMEOUT", "").strip()
+        _cron_timeout = self._parse_cron_timeout(raw)
+        assert _cron_timeout == 600.0
+
     def test_timeout_error_includes_diagnostics(self):
         """The TimeoutError message should include last activity info."""
         agent = SlowFakeAgent(