diff --git a/api/services/workflow_draft_variable_service.py b/api/services/workflow_draft_variable_service.py
index 82e8e57585..44fd72b5e4 100644
--- a/api/services/workflow_draft_variable_service.py
+++ b/api/services/workflow_draft_variable_service.py
@@ -44,6 +44,10 @@ class VariableResetError(WorkflowDraftVariableError):
     pass
 
 
+class UpdateNotSupportedError(WorkflowDraftVariableError):
+    pass
+
+
 class DraftVarLoader(VariableLoader):
     # This implements the VariableLoader interface for loading draft variables.
     #