diff --git a/util/changes.py b/util/changes.py
index 585178195..38b931f03 100644
--- a/util/changes.py
+++ b/util/changes.py
@@ -22,7 +22,7 @@ def files_and_dirs_from_tar(source_stream, removed_prefix_collector):
     # Add prefixes of removed paths to the collector.
     deleted_prefix = get_deleted_prefix(absolute)
     if deleted_prefix is not None:
-      deleted_prefix.add(deleted_prefix)
+      removed_prefix_collector.add(deleted_prefix)
       continue
 
     # Otherwise, yield the path if it is in the allowed types.