diff --git a/src/google/adk/tools/transfer_to_agent_tool.py b/src/google/adk/tools/transfer_to_agent_tool.py
index fb419dd575..bd71e3d873 100644
--- a/src/google/adk/tools/transfer_to_agent_tool.py
+++ b/src/google/adk/tools/transfer_to_agent_tool.py
@@ -74,14 +74,12 @@ def _get_declaration(self) -> Optional[types.FunctionDeclaration]:
       return function_decl
 
     # Handle parameters (types.Schema object)
-    if function_decl.parameters:
+   if function_decl.parameters and function_decl.parameters.properties:
       agent_name_schema = function_decl.parameters.properties.get('agent_name')
-      if agent_name_schema:
-        agent_name_schema.enum = self._agent_names
 
     # Handle parameters_json_schema (dict)
     if function_decl.parameters_json_schema:
-      properties = function_decl.parameters_json_schema.get('properties', {})
+      properties = function_decl.parameters_json_schema.get('properties') or {}
       if 'agent_name' in properties:
         properties['agent_name']['enum'] = self._agent_names