diff --git a/ia-upload-stream b/ia-upload-stream
index 230ae90..bdaea48 100755
--- a/ia-upload-stream
+++ b/ia-upload-stream
@@ -220,7 +220,7 @@ def main():
 	args = parser.parse_args()
 	if (args.parts or args.abort) and not args.uploadId:
 		parser.error('--parts and --abort can only be used together with --upload-id')
-	if args.uploadId and bool(args.parts) == bool(args.abort):
+	if args.uploadId and (args.parts is not None) == bool(args.abort):
 		parser.error('--upload-id requires exactly one of --parts and --abort')
 
 	logging.basicConfig(level = logging.INFO, format = '{asctime}.{msecs:03.0f}  {levelname}  {name}  {message}', datefmt = '%Y-%m-%d %H:%M:%S', style = '{')