diff --git a/jac/jaclang/runtimelib/machine.py b/jac/jaclang/runtimelib/machine.py
index 52ca0cd7e..cb45b6476 100644
--- a/jac/jaclang/runtimelib/machine.py
+++ b/jac/jaclang/runtimelib/machine.py
@@ -151,19 +151,23 @@ def update_walker(
             logger.warning(f"Module {module_name} not found in loaded modules.")
         return ()
 
-    def spawn_node(self, node_name: str, attributes: dict = {}, module_name: str = '__main__') -> NodeArchitype:
+    def spawn_node(self, node_name: str, attributes: dict = None, module_name: str = '__main__') -> NodeArchitype:
         """Spawn a node instance of the given node_name with attributes."""
         node_class = self.get_architype(module_name, node_name)
         if isinstance(node_class, type) and issubclass(node_class, NodeArchitype):
+            if attributes is None:
+                attributes = {}
             node_instance = node_class(**attributes)
             return node_instance
         else:
             raise ValueError(f"Node {node_name} not found.")
 
-    def spawn_walker(self, walker_name: str, attributes: dict = {}, module_name: str = '__main__') -> WalkerArchitype:
+    def spawn_walker(self, walker_name: str, attributes: dict = None, module_name: str = '__main__') -> WalkerArchitype:
         """Spawn a walker instance of the given walker_name."""
         walker_class = self.get_architype(module_name, walker_name)
         if isinstance(walker_class, type) and issubclass(walker_class, WalkerArchitype):
+            if attributes is None:
+                attributes = {}
             walker_instance = walker_class(**attributes)
             return walker_instance
         else: