diff --git a/litellm/proxy/management_endpoints/key_management_endpoints.py b/litellm/proxy/management_endpoints/key_management_endpoints.py
index 8b402fcff77..95ea8ad4187 100644
--- a/litellm/proxy/management_endpoints/key_management_endpoints.py
+++ b/litellm/proxy/management_endpoints/key_management_endpoints.py
@@ -512,6 +512,14 @@ async def _common_key_generation_helper(  # noqa: PLR0915
             )
             if upperbound_value is not None:
                 if value is None:
+                    if key == "duration" and key in data.model_fields_set:
+                        # Explicitly null = never expires → exceeds any finite upperbound
+                        raise HTTPException(
+                            status_code=400,
+                            detail={
+                                "error": f"{key} is over max limit set in config - user_value=null (never expires); max_value={upperbound_value}"
+                            },
+                        )
                     # Use the upperbound value if user didn't provide a value
                     setattr(data, key, upperbound_value)
                 else:
diff --git a/tests/test_litellm/enterprise/proxy/test_key_duration_ceiling.py b/tests/test_litellm/enterprise/proxy/test_key_duration_ceiling.py
index 1e6541dbcec..8be95e8cbdc 100644
--- a/tests/test_litellm/enterprise/proxy/test_key_duration_ceiling.py
+++ b/tests/test_litellm/enterprise/proxy/test_key_duration_ceiling.py
@@ -17,21 +17,27 @@ from unittest.mock import MagicMock
 
 from litellm.proxy._types import GenerateKeyRequest, LiteLLM_TeamTable
 
+_ENTERPRISE_SOURCE = os.path.normpath(
+    os.path.join(
+        os.path.dirname(__file__),
+        "..", "..", "..", "..",
+        "enterprise", "litellm_enterprise", "proxy",
+        "management_endpoints", "key_management_endpoints.py",
+    )
+)
+
+pytestmark = pytest.mark.skipif(
+    not os.path.exists(_ENTERPRISE_SOURCE),
+    reason=f"Enterprise source not available at {_ENTERPRISE_SOURCE}",
+)
+
 
 def _load_local_add_team_member_key_duration():
     """Load add_team_member_key_duration from the local enterprise source tree."""
-    local_path = os.path.normpath(
-        os.path.join(
-            os.path.dirname(__file__),
-            "..", "..", "..", "..",
-            "enterprise", "litellm_enterprise", "proxy",
-            "management_endpoints", "key_management_endpoints.py",
-        )
-    )
     module_name = "_local_enterprise_key_management_endpoints"
     # Remove cached version so we always reload from the local file
     sys.modules.pop(module_name, None)
-    spec = importlib.util.spec_from_file_location(module_name, local_path)
+    spec = importlib.util.spec_from_file_location(module_name, _ENTERPRISE_SOURCE)
     module = importlib.util.module_from_spec(spec)  # type: ignore[arg-type]
     spec.loader.exec_module(module)  # type: ignore[union-attr]
     return module.add_team_member_key_duration
@@ -109,10 +115,12 @@ class TestAddTeamMemberKeyDuration:
         assert result.duration is None
 
     def test_service_account_returns_unchanged(self):
-        """user_id=None (service account) → data is returned unchanged."""
+        """user_id=None (service account) → team duration is NOT applied."""
         fn = _load_local_add_team_member_key_duration()
 
         data = GenerateKeyRequest(user_id=None)
         result = fn(_make_team("30d"), data)
 
-        assert result.duration is None
+        # Verify the service-account guard prevented the team max from being applied
+        assert result.duration is None, "Service account should not inherit team duration"
+        assert result.duration != "30d"
diff --git a/tests/test_litellm/proxy/management_endpoints/test_key_management_endpoints.py b/tests/test_litellm/proxy/management_endpoints/test_key_management_endpoints.py
index a1605734d8e..fc2ecce9df8 100644
--- a/tests/test_litellm/proxy/management_endpoints/test_key_management_endpoints.py
+++ b/tests/test_litellm/proxy/management_endpoints/test_key_management_endpoints.py
@@ -6457,6 +6457,75 @@ class TestValidateKeyAliasFormat:
             assert "Invalid key_alias format" in str(exc.value.message)
 
 
+class TestUpperboundNullDurationValidation:
+    """Tests for upperbound validation when duration is explicitly null (never expires)."""
+
+    @pytest.mark.asyncio
+    async def test_explicit_null_duration_raises_when_upperbound_set(self):
+        """duration=null (never expires) should raise 400 when upperbound duration is set."""
+        import litellm
+        from litellm.types.proxy.management_endpoints.ui_sso import (
+            LiteLLM_UpperboundKeyGenerateParams,
+        )
+
+        original = litellm.upperbound_key_generate_params
+        try:
+            litellm.upperbound_key_generate_params = (
+                LiteLLM_UpperboundKeyGenerateParams(duration="30d")
+            )
+            with pytest.raises(HTTPException) as exc_info:
+                await _common_key_generation_helper(
+                    data=GenerateKeyRequest(user_id="user-1", duration=None),
+                    user_api_key_dict=UserAPIKeyAuth(
+                        user_role=LitellmUserRoles.PROXY_ADMIN, api_key="sk-1"
+                    ),
+                    litellm_changed_by=None,
+                    team_table=None,
+                )
+            assert exc_info.value.status_code == 400
+            assert "never expires" in str(exc_info.value.detail).lower()
+        finally:
+            litellm.upperbound_key_generate_params = original
+
+    @pytest.mark.asyncio
+    async def test_omitted_duration_uses_upperbound_as_default(self):
+        """Duration not sent → upperbound is applied as default (no error)."""
+        import litellm
+        from litellm.types.proxy.management_endpoints.ui_sso import (
+            LiteLLM_UpperboundKeyGenerateParams,
+        )
+
+        original = litellm.upperbound_key_generate_params
+        try:
+            litellm.upperbound_key_generate_params = (
+                LiteLLM_UpperboundKeyGenerateParams(duration="30d")
+            )
+            with patch(
+                "litellm.proxy.management_endpoints.key_management_endpoints.generate_key_helper_fn",
+                new_callable=AsyncMock,
+                return_value={
+                    "key": "sk-test",
+                    "expires": None,
+                    "user_id": "user-1",
+                },
+            ), patch("litellm.proxy.proxy_server.prisma_client"), patch(
+                "litellm.proxy.proxy_server.llm_router"
+            ), patch(
+                "litellm.proxy.proxy_server.premium_user", False
+            ):
+                # Should not raise — duration omitted, so upperbound fills in as default
+                await _common_key_generation_helper(
+                    data=GenerateKeyRequest(user_id="user-1"),
+                    user_api_key_dict=UserAPIKeyAuth(
+                        user_role=LitellmUserRoles.PROXY_ADMIN, api_key="sk-1"
+                    ),
+                    litellm_changed_by=None,
+                    team_table=None,
+                )
+        finally:
+            litellm.upperbound_key_generate_params = original
+
+
 class TestCommonKeyGenerationHelperTeamDurationValidation:
     """Tests for team duration validation inside _common_key_generation_helper."""