diff --git a/src/python_workflow_definition/models.py b/src/python_workflow_definition/models.py
index 8b25be8..c78dc73 100644
--- a/src/python_workflow_definition/models.py
+++ b/src/python_workflow_definition/models.py
@@ -28,6 +28,11 @@
     "PythonWorkflowDefinitionWorkflow",
 )
 
+JsonPrimitive = Union[str, int, float, bool, None]
+AllowableDefaults = TypeAliasType(
+    "AllowableDefaults", "Union[JsonPrimitive, tuple[AllowableDefaults, ...]]"
+)
+
 
 JsonPrimitive = Union[str, int, float, bool, None]
 AllowableDefaults = TypeAliasType(
diff --git a/tests/test_models.py b/tests/test_models.py
index d353f46..c3c1e65 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -53,8 +53,8 @@ def test_input_node_valid_values(self):
             "string",
             True,
             None,
-            [1, 2],
-            [["recursive", "tuple"], [True, False]],
+            (1, 2),
+            (("recursive", "tuple"), (True, False)),
         )
         for value in good_values:
             with self.subTest(value=value):
@@ -73,9 +73,10 @@ def test_input_node_valid_values(self):
                     ).value
                 )
 
+
     def test_input_node_invalid_value_raises(self):
         bad_values = (
-            {1: 2},
+            {"mutable": "thing"},
             _NoTrivialSerialization(),
         )
         for value in bad_values: