diff --git a/src/borg/archive.py b/src/borg/archive.py
index a32d10e51..d3d0a3431 100644
--- a/src/borg/archive.py
+++ b/src/borg/archive.py
@@ -936,7 +936,7 @@ Utilization of max. archive size: {csize_max:.0%}
                 # 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:
                 for chunk in item.chunks:
-                    cache.chunk_incref(chunk.id, stats)
+                    cache.chunk_incref(chunk.id, stats, size_=chunk.size)
 
     def process_stdin(self, path, cache):
         uid, gid = 0, 0
diff --git a/src/borg/cache.py b/src/borg/cache.py
index fb113d93d..520e66a9d 100644
--- a/src/borg/cache.py
+++ b/src/borg/cache.py
@@ -877,7 +877,7 @@ class LocalCache(CacheStatsMixin):
                             id, stored_size, size))
         return refcount
 
-    def chunk_incref(self, id, stats):
+    def chunk_incref(self, id, stats, size_=None):
         if not self.txn_active:
             self.begin_txn()
         count, size, csize = self.chunks.incref(id)