diff --git a/src/borg/archive.py b/src/borg/archive.py
index 98a6e2510..6a1aae4d5 100644
--- a/src/borg/archive.py
+++ b/src/borg/archive.py
@@ -942,8 +942,9 @@ def chunk_processor(data):
 
                 # if we created part files, we have referenced all chunks from the part files,
                 # but we also will reference the same chunks also from the final, complete file:
+                dummy_stats = Statistics()  # do not count this data volume twice
                 for chunk in item.chunks:
-                    cache.chunk_incref(chunk.id, stats, size=chunk.size)
+                    cache.chunk_incref(chunk.id, dummy_stats, size=chunk.size)
 
     def process_stdin(self, path, cache):
         uid, gid = 0, 0