diff --git a/sshuttle/options.py b/sshuttle/options.py
index baf10ec..9eec931 100644
--- a/sshuttle/options.py
+++ b/sshuttle/options.py
@@ -270,6 +270,7 @@ parser.add_argument(
     metavar="PATH",
     action=Concat,
     dest="subnets_file",
+    default=[],
     type=parse_subnet_file,
     help="""
     file where the subnets are stored, instead of on the command line