diff --git a/table/cuckoo_table_builder.cc b/table/cuckoo_table_builder.cc
index e107071f2ab2f3239908fe6be5d3cb4e33ed1f30..1cf19e3aacf84cdd582e046e78d41d3ed0373868 100644
--- a/table/cuckoo_table_builder.cc
+++ b/table/cuckoo_table_builder.cc
@@ -323,7 +323,7 @@ uint64_t CuckooTableBuilder::FileSize() const {
     expected_hash_table_size *= 2;
   }
   return (kvs_[0].first.size() + kvs_[0].second.size()) *
-    expected_hash_table_size;
+    expected_hash_table_size - 1;
 }
 
 // This method is invoked when there is no place to insert the target key.