diff --git a/httpie/cli.py b/httpie/cli.py
index 91d53472..e78b59f2 100644
--- a/httpie/cli.py
+++ b/httpie/cli.py
@@ -102,6 +102,7 @@ positional.add_argument(
     'items',
     metavar='REQUEST_ITEM',
     nargs=ZERO_OR_MORE,
+    default=None,
     type=KeyValueArgType(*SEP_GROUP_ALL_ITEMS),
     help=r"""
     Optional key-value pairs to be included in the request. The separator used