diff --git a/requirements.txt b/requirements.txt
index 46836ef..d3f0e9d 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -11,4 +11,4 @@ pydantic-settings>=2.0.0
 python-dotenv>=1.0.0
 sniffio>=1.3.0
 iptocc>=0.1.0
-phonenumberslite
+phonenumberslite>=9.0
diff --git a/tests/test_ip_service.py b/tests/test_ip_service.py
index 6d6a06c..85a52d2 100644
--- a/tests/test_ip_service.py
+++ b/tests/test_ip_service.py
@@ -11,3 +11,8 @@ def test_country_names_ca_bug_fixed():
     from app.services import ip_service
     assert ip_service.COUNTRY_NAMES.get("CA") == "加拿大"
     assert ip_service.COUNTRY_NAMES.get("AU") == "澳大利亚"
+
+
+def test_resolve_region_code_known_ip_deterministic():
+    from app.services.ip_service import resolve_region_code
+    assert resolve_region_code("8.8.8.8") == "US"   # Google DNS, 离线库确定性