diff --git a/src/langbot/pkg/provider/modelmgr/token.py b/src/langbot/pkg/provider/modelmgr/token.py
index 51e97956..e677829a 100644
--- a/src/langbot/pkg/provider/modelmgr/token.py
+++ b/src/langbot/pkg/provider/modelmgr/token.py
@@ -30,4 +30,6 @@ class TokenManager:
         return self.tokens[self.using_token_index]
 
     def next_token(self):
+        if len(self.tokens) == 0:
+            return
         self.using_token_index = (self.using_token_index + 1) % len(self.tokens)
diff --git a/tests/unit_tests/provider/test_model_service.py b/tests/unit_tests/provider/test_model_service.py
index dab68043..344cfe39 100644
--- a/tests/unit_tests/provider/test_model_service.py
+++ b/tests/unit_tests/provider/test_model_service.py
@@ -81,6 +81,15 @@ def test_token_manager_filters_blank_and_duplicate_tokens():
     assert token_mgr.get_token() == 'first-key'
 
 
+def test_token_manager_next_token_ignores_empty_token_list():
+    token_mgr = TokenManager('provider-uuid', [])
+
+    token_mgr.next_token()
+
+    assert token_mgr.get_token() == ''
+    assert token_mgr.using_token_index == 0
+
+
 @pytest.mark.asyncio
 async def test_openai_requester_initialize_uses_placeholder_api_key(monkeypatch):
     captured_kwargs = {}