diff --git a/docs/changelog/1418.feature.rst b/docs/changelog/1418.feature.rst
new file mode 100644
index 000000000..f08283090
--- /dev/null
+++ b/docs/changelog/1418.feature.rst
@@ -0,0 +1 @@
+Allow parallel mode without arguments. - by :user:`ssbarnea`
diff --git a/src/tox/config/parallel.py b/src/tox/config/parallel.py
index ca0dbbd51..1519d58a8 100644
--- a/src/tox/config/parallel.py
+++ b/src/tox/config/parallel.py
@@ -45,9 +45,11 @@ def add_parallel_flags(parser):
     parser.add_argument(
         "-p",
         "--parallel",
+        nargs="?",
+        const="auto",
         dest="parallel",
         help="run tox environments in parallel, the argument controls limit: all,"
-        " auto - cpu count, some positive number, zero is turn off",
+        " auto or missing argument - cpu count, some positive number, 0 to turn off",
         action="store",
         type=parse_num_processes,
         default=DEFAULT_PARALLEL,