diff --git a/pyproject.toml b/pyproject.toml
index a815f66af..d2be96b23 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -51,7 +51,7 @@ dependencies = [
     "filelock>=3.25.2",
     "watchfiles>=1.1.1,<2.0.0",
     "packaging>=24.0",
-    "tzdata>=2025.2; sys_platform == 'win32'",
+    "tzdata>=2025.2",
     "defusedxml>=0.7.1,<1.0.0",
     "pypdf>=5.0.0,<6.0.0",
     "python-docx>=1.1.0,<2.0.0",
diff --git a/tests/channels/test_channel_plugins.py b/tests/channels/test_channel_plugins.py
index fb904be35..fea682081 100644
--- a/tests/channels/test_channel_plugins.py
+++ b/tests/channels/test_channel_plugins.py
@@ -2558,7 +2558,7 @@ def test_optional_dependency_metadata_for_enable():
     ):
         assert not any(dep.startswith(dep_name) for dep in required)
     for dependency in (
-        "tzdata>=2025.2; sys_platform == 'win32'",
+        "tzdata>=2025.2",
         "defusedxml>=0.7.1,<1.0.0",
         "pypdf>=5.0.0,<6.0.0",
         "python-docx>=1.1.0,<2.0.0",
diff --git a/tests/config/test_model_presets.py b/tests/config/test_model_presets.py
index 726a8f793..e419e40e8 100644
--- a/tests/config/test_model_presets.py
+++ b/tests/config/test_model_presets.py
@@ -1,4 +1,8 @@
 import json
+import os
+import subprocess
+import sys
+import textwrap
 import warnings
 
 import pytest
@@ -42,6 +46,32 @@ def test_agent_timezone_rejects_unknown_iana_name() -> None:
         Config.model_validate({"agents": {"defaults": {"timezone": "Not/AZone"}}})
 
 
+def test_agent_timezones_use_packaged_data_without_system_database() -> None:
+    script = textwrap.dedent(
+        """\
+        from zoneinfo import TZPATH
+
+        from nanobot.config.schema import Config
+
+        assert not TZPATH
+        for name in ("UTC", "Asia/Shanghai"):
+            config = Config.model_validate({"agents": {"defaults": {"timezone": name}}})
+            serialized = config.model_dump(mode="json", by_alias=True)
+            restored = Config.model_validate(serialized)
+            assert restored.agents.defaults.timezone == name
+        """
+    )
+    result = subprocess.run(
+        [sys.executable, "-c", script],
+        env=os.environ | {"PYTHONTZPATH": ""},
+        capture_output=True,
+        text=True,
+        check=False,
+    )
+
+    assert result.returncode == 0, result.stderr
+
+
 def test_provider_api_type_accepts_exact_values_only() -> None:
     config = Config.model_validate({
         "providers": {