diff --git a/tableauserverclient/models/project_item.py b/tableauserverclient/models/project_item.py
index 48f27c60..b20cb537 100644
--- a/tableauserverclient/models/project_item.py
+++ b/tableauserverclient/models/project_item.py
@@ -174,7 +174,7 @@ def _set_permissions(self, permissions):
         self._permissions = permissions
 
     def _set_default_permissions(self, permissions, content_type):
-        attr = f"_default_{content_type}_permissions"
+        attr = f"_default_{content_type}_permissions".lower()
         setattr(
             self,
             attr,