diff --git a/nanobot/cli/commands.py b/nanobot/cli/commands.py
index b61d9aa..668fcb5 100644
--- a/nanobot/cli/commands.py
+++ b/nanobot/cli/commands.py
@@ -787,15 +787,19 @@ def cron_add(
     store_path = get_data_dir() / "cron" / "jobs.json"
     service = CronService(store_path)
     
-    job = service.add_job(
-        name=name,
-        schedule=schedule,
-        message=message,
-        deliver=deliver,
-        to=to,
-        channel=channel,
-    )
-    
+    try:
+        job = service.add_job(
+            name=name,
+            schedule=schedule,
+            message=message,
+            deliver=deliver,
+            to=to,
+            channel=channel,
+        )
+    except ValueError as e:
+        console.print(f"[red]Error: {e}[/red]")
+        raise typer.Exit(1) from e
+
     console.print(f"[green]✓[/green] Added job '{job.name}' ({job.id})")
 
 
diff --git a/nanobot/cron/service.py b/nanobot/cron/service.py
index 14666e8..7ae1153 100644
--- a/nanobot/cron/service.py
+++ b/nanobot/cron/service.py
@@ -45,6 +45,20 @@ def _compute_next_run(schedule: CronSchedule, now_ms: int) -> int | None:
     return None
 
 
+def _validate_schedule_for_add(schedule: CronSchedule) -> None:
+    """Validate schedule fields that would otherwise create non-runnable jobs."""
+    if schedule.tz and schedule.kind != "cron":
+        raise ValueError("tz can only be used with cron schedules")
+
+    if schedule.kind == "cron" and schedule.tz:
+        try:
+            from zoneinfo import ZoneInfo
+
+            ZoneInfo(schedule.tz)
+        except Exception:
+            raise ValueError(f"unknown timezone '{schedule.tz}'") from None
+
+
 class CronService:
     """Service for managing and executing scheduled jobs."""
     
@@ -272,6 +286,7 @@ class CronService:
     ) -> CronJob:
         """Add a new job."""
         store = self._load_store()
+        _validate_schedule_for_add(schedule)
         now = _now_ms()
         
         job = CronJob(
diff --git a/tests/test_cron_commands.py b/tests/test_cron_commands.py
new file mode 100644
index 0000000..bce1ef5
--- /dev/null
+++ b/tests/test_cron_commands.py
@@ -0,0 +1,29 @@
+from typer.testing import CliRunner
+
+from nanobot.cli.commands import app
+
+runner = CliRunner()
+
+
+def test_cron_add_rejects_invalid_timezone(monkeypatch, tmp_path) -> None:
+    monkeypatch.setattr("nanobot.config.loader.get_data_dir", lambda: tmp_path)
+
+    result = runner.invoke(
+        app,
+        [
+            "cron",
+            "add",
+            "--name",
+            "demo",
+            "--message",
+            "hello",
+            "--cron",
+            "0 9 * * *",
+            "--tz",
+            "America/Vancovuer",
+        ],
+    )
+
+    assert result.exit_code == 1
+    assert "Error: unknown timezone 'America/Vancovuer'" in result.stdout
+    assert not (tmp_path / "cron" / "jobs.json").exists()
diff --git a/tests/test_cron_service.py b/tests/test_cron_service.py
new file mode 100644
index 0000000..07e990a
--- /dev/null
+++ b/tests/test_cron_service.py
@@ -0,0 +1,30 @@
+import pytest
+
+from nanobot.cron.service import CronService
+from nanobot.cron.types import CronSchedule
+
+
+def test_add_job_rejects_unknown_timezone(tmp_path) -> None:
+    service = CronService(tmp_path / "cron" / "jobs.json")
+
+    with pytest.raises(ValueError, match="unknown timezone 'America/Vancovuer'"):
+        service.add_job(
+            name="tz typo",
+            schedule=CronSchedule(kind="cron", expr="0 9 * * *", tz="America/Vancovuer"),
+            message="hello",
+        )
+
+    assert service.list_jobs(include_disabled=True) == []
+
+
+def test_add_job_accepts_valid_timezone(tmp_path) -> None:
+    service = CronService(tmp_path / "cron" / "jobs.json")
+
+    job = service.add_job(
+        name="tz ok",
+        schedule=CronSchedule(kind="cron", expr="0 9 * * *", tz="America/Vancouver"),
+        message="hello",
+    )
+
+    assert job.schedule.tz == "America/Vancouver"
+    assert job.state.next_run_at_ms is not None