diff --git a/plugins/3MFWriter/ThreeMFWorkspaceWriter.py b/plugins/3MFWriter/ThreeMFWorkspaceWriter.py
index 9c143f0057..0fffe693cc 100644
--- a/plugins/3MFWriter/ThreeMFWorkspaceWriter.py
+++ b/plugins/3MFWriter/ThreeMFWorkspaceWriter.py
@@ -95,7 +95,7 @@ class ThreeMFWorkspaceWriter(WorkspaceWriter):
         file_in_archive.compress_type = zipfile.ZIP_DEFLATED
 
         # Do not include the network authentication keys
-        ignore_keys = ["network_authentication_id", "network_authentication_key"]
+        ignore_keys = {"network_authentication_id", "network_authentication_key"}
         serialized_data = container.serialize(ignored_metadata_keys = ignore_keys)
 
         archive.writestr(file_in_archive, serialized_data)
diff --git a/plugins/XmlMaterialProfile/XmlMaterialProfile.py b/plugins/XmlMaterialProfile/XmlMaterialProfile.py
index 4dc955db42..dd07ec73e8 100644
--- a/plugins/XmlMaterialProfile/XmlMaterialProfile.py
+++ b/plugins/XmlMaterialProfile/XmlMaterialProfile.py
@@ -97,7 +97,7 @@ class XmlMaterialProfile(InstanceContainer):
     ##  Overridden from InstanceContainer
     # base file: common settings + supported machines
     # machine / variant combination: only changes for itself.
-    def serialize(self, ignored_metadata_keys: Optional[List] = None):
+    def serialize(self, ignored_metadata_keys: Optional[set] = None):
         registry = ContainerRegistry.getInstance()
 
         base_file = self.getMetaDataEntry("base_file", "")
@@ -119,8 +119,8 @@ class XmlMaterialProfile(InstanceContainer):
         metadata = copy.deepcopy(self.getMetaData())
         # setting_version is derived from the "version" tag in the schema, so don't serialize it into a file
         if ignored_metadata_keys is None:
-            ignored_metadata_keys = []
-        ignored_metadata_keys = ignored_metadata_keys + ["setting_version"]
+            ignored_metadata_keys = set()
+        ignored_metadata_keys |= {"setting_version"}
         # remove the keys that we want to ignore in the metadata
         for key in ignored_metadata_keys:
             if key in metadata: