diff --git a/tools/releasetools/validate_target_files.py b/tools/releasetools/validate_target_files.py
index 37d5d27..5d99c99 100755
--- a/tools/releasetools/validate_target_files.py
+++ b/tools/releasetools/validate_target_files.py
@@ -44,7 +44,7 @@
   """Constructs and returns a File object. Rounds up its size if needed."""
 
   assert os.path.exists(unpacked_name)
-  with open(unpacked_name, 'r') as f:
+  with open(unpacked_name, 'rb') as f:
     file_data = f.read()
   file_size = len(file_data)
   if round_up: