diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index fad6a5e..5f81d53 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -1203,10 +1203,11 @@
     return self._DoCall("VerifyOTA_Assertions")
 
 class File(object):
-  def __init__(self, name, data):
+  def __init__(self, name, data, compress_size = None):
     self.name = name
     self.data = data
     self.size = len(data)
+    self.compress_size = compress_size or self.size
     self.sha1 = sha1(data).hexdigest()
 
   @classmethod