diff --git a/shierfeng-fastapi-backend/module_business/domain/pallet_state_machine.py b/shierfeng-fastapi-backend/module_business/domain/pallet_state_machine.py
index 6b08a3f..d8e8e52 100644
--- a/shierfeng-fastapi-backend/module_business/domain/pallet_state_machine.py
+++ b/shierfeng-fastapi-backend/module_business/domain/pallet_state_machine.py
@@ -32,7 +32,8 @@ class PalletStateMachine:
         current: PalletFlowState,
         target: PalletFlowState,
     ) -> None:
+        if not isinstance(current, PalletFlowState) or not isinstance(target, PalletFlowState):
+            raise TypeError('current 和 target 必须是 PalletFlowState')
+
         if (current, target) not in cls._ALLOWED_TRANSITIONS:
-            raise InvalidPalletTransition(
-                f'不允许的托盘状态迁移：{current.value} -> {target.value}'
-            )
+            raise InvalidPalletTransition(f'不允许的托盘状态迁移：{current.value} -> {target.value}')
diff --git a/shierfeng-fastapi-backend/tests/module_business/test_state_machine.py b/shierfeng-fastapi-backend/tests/module_business/test_state_machine.py
index 9fb125b..3bebc13 100644
--- a/shierfeng-fastapi-backend/tests/module_business/test_state_machine.py
+++ b/shierfeng-fastapi-backend/tests/module_business/test_state_machine.py
@@ -39,6 +39,22 @@ class PalletStateMachineTest(unittest.TestCase):
                 PalletFlowState.FILLED_IN_WAREHOUSE,
             )
 
+    def test_raw_string_states_are_rejected(self) -> None:
+        with self.assertRaisesRegex(TypeError, 'PalletFlowState'):
+            PalletStateMachine.ensure_transition(
+                'UNSTOCKED',
+                'EMPTY_IN_WAREHOUSE',
+            )
+
+    def test_mixed_state_types_are_rejected(self) -> None:
+        mixed_states = (
+            ('UNSTOCKED', PalletFlowState.EMPTY_IN_WAREHOUSE),
+            (PalletFlowState.UNSTOCKED, 'EMPTY_IN_WAREHOUSE'),
+        )
+        for current, target in mixed_states:
+            with self.subTest(current=current, target=target), self.assertRaisesRegex(TypeError, 'PalletFlowState'):
+                PalletStateMachine.ensure_transition(current, target)
+
     def test_confirmed_flow_is_the_only_allowed_transition_set(self) -> None:
         actual_allowed = set()
         for current in PalletFlowState:
@@ -54,6 +70,18 @@ class PalletStateMachineTest(unittest.TestCase):
 
 class PalletEnumTest(unittest.TestCase):
     def test_supporting_enum_values_match_domain_contract(self) -> None:
+        self.assertEqual(
+            [
+                'UNSTOCKED',
+                'EMPTY_IN_WAREHOUSE',
+                'FILLED_IN_WAREHOUSE',
+                'AT_SITE_UNUSED',
+                'AT_SITE_PARTIAL',
+                'AT_SITE_EMPTY',
+                'RETURNING',
+            ],
+            [item.value for item in PalletFlowState],
+        )
         self.assertEqual(['DRAFT', 'CONFIRMED'], [item.value for item in DocumentStatus])
         self.assertEqual(
             ['REQUESTED', 'CONFIRMED'],