diff --git a/novaclient/tests/unit/v2/test_shell.py b/novaclient/tests/unit/v2/test_shell.py
index b1b9b8085..9b3728e0b 100644
--- a/novaclient/tests/unit/v2/test_shell.py
+++ b/novaclient/tests/unit/v2/test_shell.py
@@ -16,6 +16,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import argparse
 import base64
 import datetime
 import os
@@ -686,6 +687,10 @@ class ShellTest(utils.TestCase):
                 }
             }, pos=4)
 
+    def test_boot_invalid_ephemeral_data_format(self):
+        cmd = 'boot --flavor 1 --image 1 --ephemeral 1 some-server'
+        self.assertRaises(argparse.ArgumentTypeError, self.run_command, cmd)
+
     def test_flavor_list(self):
         self.run_command('flavor-list')
         self.assert_called_anytime('GET', '/flavors/detail')
diff --git a/novaclient/v2/shell.py b/novaclient/v2/shell.py
index 33653a121..d3108a941 100644
--- a/novaclient/v2/shell.py
+++ b/novaclient/v2/shell.py
@@ -118,8 +118,11 @@ def _parse_block_device_mapping_v2(args, image):
     for ephemeral_spec in args.ephemeral:
         bdm_dict = {'source_type': 'blank', 'destination_type': 'local',
                     'boot_index': -1, 'delete_on_termination': True}
-
-        eph_dict = dict(v.split('=') for v in ephemeral_spec.split(','))
+        try:
+            eph_dict = dict(v.split('=') for v in ephemeral_spec.split(','))
+        except ValueError:
+            err_msg = (_("Invalid ephemeral argument '%s'.") % args.ephemeral)
+            raise argparse.ArgumentTypeError(err_msg)
         if 'size' in eph_dict:
             bdm_dict['volume_size'] = eph_dict['size']
         if 'format' in eph_dict: