diff --git a/tools/releasetools/sign_apex.py b/tools/releasetools/sign_apex.py
index 679f57a..66f5e05 100755
--- a/tools/releasetools/sign_apex.py
+++ b/tools/releasetools/sign_apex.py
@@ -141,7 +141,7 @@
       signing_args=options.get('payload_extra_args'),
       codename_to_api_level_map=options.get(
           'codename_to_api_level_map', {}),
-      sign_tool=options['sign_tool'])
+      sign_tool=options.get('sign_tool', None))
   shutil.copyfile(signed_apex, args[1])
   logger.info("done.")