diff --git a/tools/releasetools/blockimgdiff.py b/tools/releasetools/blockimgdiff.py
index cb6fc8582..a6c6bd874 100644
--- a/tools/releasetools/blockimgdiff.py
+++ b/tools/releasetools/blockimgdiff.py
@@ -483,7 +483,7 @@ class BlockImageDiff(object):
       if free_string:
         out.append("".join(free_string))
 
-      if self.version >= 2:
+      if self.version >= 2 and common.OPTIONS.cache_size is not None:
         # Sanity check: abort if we're going to need more stash space than
         # the allowed size (cache_size * threshold). There are two purposes
         # of having a threshold here. a) Part of the cache may have been
@@ -524,10 +524,16 @@ class BlockImageDiff(object):
 
     if self.version >= 2:
       max_stashed_size = max_stashed_blocks * self.tgt.blocksize
-      max_allowed = common.OPTIONS.cache_size * common.OPTIONS.stash_threshold
-      print("max stashed blocks: %d  (%d bytes), limit: %d bytes (%.2f%%)\n" % (
-          max_stashed_blocks, max_stashed_size, max_allowed,
-          max_stashed_size * 100.0 / max_allowed))
+      OPTIONS = common.OPTIONS
+      if OPTIONS.cache_size is not None:
+        max_allowed = OPTIONS.cache_size * OPTIONS.stash_threshold
+        print("max stashed blocks: %d  (%d bytes), "
+              "limit: %d bytes (%.2f%%)\n" % (
+              max_stashed_blocks, max_stashed_size, max_allowed,
+              max_stashed_size * 100.0 / max_allowed))
+      else:
+        print("max stashed blocks: %d  (%d bytes), limit: <unknown>\n" % (
+              max_stashed_blocks, max_stashed_size))
 
   def ReviseStashSize(self):
     print("Revising stash size...")
diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index 2965fa804..0e8923b4a 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -62,6 +62,9 @@ class Options(object):
     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()
diff --git a/tools/releasetools/ota_from_target_files.py b/tools/releasetools/ota_from_target_files.py
index c5c16b408..7a470e927 100755
--- a/tools/releasetools/ota_from_target_files.py
+++ b/tools/releasetools/ota_from_target_files.py
@@ -1634,7 +1634,7 @@ def main(argv):
 
     cache_size = OPTIONS.info_dict.get("cache_size", None)
     if cache_size is None:
-      raise RuntimeError("can't determine the cache partition size")
+      print "--- can't determine the cache partition size ---"
     OPTIONS.cache_size = cache_size
 
     if OPTIONS.incremental_source is None: