diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index 3f3b011..4f24ad5 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -990,7 +990,7 @@
   return args
 
 
-def MakeTempFile(prefix=None, suffix=None):
+def MakeTempFile(prefix='tmp', suffix=''):
   """Make a temp file and add it to the list of things to be deleted
   when Cleanup() is called.  Return the filename."""
   fd, fn = tempfile.mkstemp(prefix=prefix, suffix=suffix)