diff --git a/__init__.py b/__init__.py
index 01c0427..d730115 100755
--- a/__init__.py
+++ b/__init__.py
@@ -1995,7 +1995,7 @@ def _dispatch_batches(
         for item in item_list:
             if prep_args is not None:
                 # Insert the given item as the first argument to be passed to the _prep function determined above
-                prep_args[0] = item
+                prep_args[0] = { "$distinct_id": item }
                 params = prep_function(*prep_args)
                 if params:
                     batch.append(params)