diff --git a/tildes/scripts/clean_private_data.py b/tildes/scripts/clean_private_data.py
index 79e9284..5f8a3f2 100644
--- a/tildes/scripts/clean_private_data.py
+++ b/tildes/scripts/clean_private_data.py
@@ -89,7 +89,9 @@ class DataCleaner():
         updated = (
             self.db_session.query(Comment)
             .filter(
-                Comment.deleted_time <= self.retention_cutoff)  # type: ignore
+                Comment.deleted_time <= self.retention_cutoff,  # type: ignore
+                Comment.user_id != 0,
+            )
             .update({
                 'user_id': 0,
                 'markdown': '',
@@ -108,7 +110,9 @@ class DataCleaner():
         updated = (
             self.db_session.query(Topic)
             .filter(
-                Topic.deleted_time <= self.retention_cutoff)  # type: ignore
+                Topic.deleted_time <= self.retention_cutoff,  # type: ignore
+                Topic.user_id != 0,
+            )
             .update({
                 'user_id': 0,
                 'title': '',