diff --git a/novaclient/shell.py b/novaclient/shell.py
index a81db89a8..7762be9b3 100644
--- a/novaclient/shell.py
+++ b/novaclient/shell.py
@@ -365,6 +365,9 @@ class OpenStackComputeShell(object):
             help=_("Use this API endpoint instead of the Service Catalog. "
                    "Defaults to env[OS_ENDPOINT_OVERRIDE]."))
 
+        parser.set_defaults(func=self.do_help)
+        parser.set_defaults(command='')
+
         if osprofiler_profiler:
             parser.add_argument('--profile',
                                 metavar='HMAC_KEY',
diff --git a/novaclient/tests/unit/test_shell.py b/novaclient/tests/unit/test_shell.py
index 889916ea7..641952910 100644
--- a/novaclient/tests/unit/test_shell.py
+++ b/novaclient/tests/unit/test_shell.py
@@ -451,6 +451,9 @@ class ShellTest(utils.TestCase):
     def test_help_no_options(self):
         self._test_help('')
 
+    def test_help_no_subcommand(self):
+        self._test_help('--os-compute-api-version 2.87')
+
     def test_help_on_subcommand(self):
         required = [
             '.*?^usage: nova set-password',
diff --git a/releasenotes/notes/fix-raw-python-error-debd3edb17c2f675.yaml b/releasenotes/notes/fix-raw-python-error-debd3edb17c2f675.yaml
new file mode 100644
index 000000000..7686ecbeb
--- /dev/null
+++ b/releasenotes/notes/fix-raw-python-error-debd3edb17c2f675.yaml
@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    `Bug #1903727 <https://bugs.launchpad.net/python-novaclient/+bug/1903727>`_:
+    Fixed raw Python error message when using ``nova`` without
+    a subcommand while passing an optional argument, such as
+    ``--os-compute-api-version 2.87``.