diff --git a/ms_agent/cron/parser.py b/ms_agent/cron/parser.py
index fcf3675d3..fc4969f8a 100644
--- a/ms_agent/cron/parser.py
+++ b/ms_agent/cron/parser.py
@@ -93,6 +93,10 @@ def parse_schedule(schedule_str: str,
 
     # 2. Try ISO timestamp for one-shot: "2025-01-01T09:00:00"
     if _ISO_RE.match(raw):
+        try:
+            datetime.fromisoformat(raw)
+        except ValueError as exc:
+            raise ValueError(f'Invalid ISO timestamp: {raw!r}') from exc
         return CronSchedule(
             kind='once',
             run_at=raw,
diff --git a/tests/cron/test_manager.py b/tests/cron/test_manager.py
index ddcaa774f..864102ea3 100644
--- a/tests/cron/test_manager.py
+++ b/tests/cron/test_manager.py
@@ -17,6 +17,11 @@ def manager(workspace):
 
 
 class TestJobManagerCRUD:
+    def test_invalid_once_schedule_is_not_saved(self, manager):
+        with pytest.raises(ValueError, match='Invalid ISO timestamp'):
+            manager.create_job(schedule_str='2025-02-30T09:00:00', prompt='invalid date')
+        assert manager.list_jobs() == []
+
     def test_create_job(self, manager):
         job = manager.create_job(schedule_str='every 60s', prompt='hello', name='Test')
         assert job.id
diff --git a/tests/cron/test_parser.py b/tests/cron/test_parser.py
index 56a873e20..3b33dfac5 100644
--- a/tests/cron/test_parser.py
+++ b/tests/cron/test_parser.py
@@ -64,6 +64,28 @@ def test_case_insensitive(self):
 
 
 class TestParseScheduleOnce:
+    @pytest.mark.parametrize('timestamp', [
+        '2025-02-29T09:00:00',
+        '2025-13-01T09:00:00',
+        '2025-06-01T24:00:00',
+        '2025-06-01T09:60:00',
+        '2025-06-01T09:00:60',
+        '2025-06-01T09:00:00invalid',
+    ])
+    def test_invalid_iso_timestamp_rejected(self, timestamp):
+        with pytest.raises(ValueError, match='Invalid ISO timestamp'):
+            parse_schedule(timestamp)
+
+    @pytest.mark.parametrize('timestamp', [
+        '2028-02-29T09:00:00',
+        '2025-06-01T09:00:00.123456+08:00',
+        '2025-06-01 09:00:00-05:30',
+    ])
+    def test_valid_iso_timestamp_preserved(self, timestamp):
+        result = parse_schedule(timestamp)
+        assert result.kind == 'once'
+        assert result.run_at == timestamp
+
     def test_iso_timestamp(self):
         result = parse_schedule('2025-06-01T09:00:00')
         assert result.kind == 'once'