diff --git a/guix-data-service/data-deletion.scm b/guix-data-service/data-deletion.scm
index 0f64da7..3b6dbd0 100644
--- a/guix-data-service/data-deletion.scm
+++ b/guix-data-service/data-deletion.scm
@@ -435,10 +435,9 @@ DELETE FROM derivation_source_files
 WHERE id IN (
   SELECT id
   FROM derivation_source_files
-  WHERE NOT EXISTS (
-    SELECT 1
+  WHERE id NOT IN (
+    SELECT derivation_source_file_id
     FROM derivation_sources
-    WHERE derivation_source_file_id = derivation_source_files.id
   )
   LIMIT 100
 )