diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index 2965fa8..0e8923b 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -62,6 +62,9 @@
     self.source_info_dict = None
     self.target_info_dict = None
     self.worker_threads = None
+    # Stash size cannot exceed cache_size * threshold.
+    self.cache_size = None
+    self.stash_threshold = 0.8
 
 
 OPTIONS = Options()