diff --git a/unit_tests/charm_tests/test_utils.py b/unit_tests/charm_tests/test_utils.py
index 280e2e2..a415360 100644
--- a/unit_tests/charm_tests/test_utils.py
+++ b/unit_tests/charm_tests/test_utils.py
@@ -30,3 +30,15 @@ class TestOpenStackBaseTest(unittest.TestCase):
 
         MyTestClass.setUpClass('foo', 'bar')
         _setUpClass.assert_called_with('foo', 'bar')
+
+
+class TestUtils(unittest.TestCase):
+
+    def test_format_addr(self):
+        self.assertEquals('1.2.3.4', test_utils.format_addr('1.2.3.4'))
+        self.assertEquals(
+            '[2001:db8::42]', test_utils.format_addr('2001:db8::42'))
+        with self.assertRaises(ValueError):
+            test_utils.format_addr('999.999.999.999')
+        with self.assertRaises(ValueError):
+            test_utils.format_addr('2001:db8::g')
diff --git a/zaza/openstack/charm_tests/test_utils.py b/zaza/openstack/charm_tests/test_utils.py
index bcb5aff..47c12d7 100644
--- a/zaza/openstack/charm_tests/test_utils.py
+++ b/zaza/openstack/charm_tests/test_utils.py
@@ -14,6 +14,7 @@
 """Module containing base class for implementing charm tests."""
 import contextlib
 import logging
+import ipaddress
 import subprocess
 import unittest
 
@@ -431,3 +432,20 @@ class OpenStackBaseTest(BaseCharmTest):
         cls.keystone_session = openstack_utils.get_overcloud_keystone_session(
             model_name=cls.model_name)
         cls.cacert = openstack_utils.get_cacert()
+
+
+def format_addr(addr):
+    """Validate and format IP address.
+
+    :param addr: IPv6 or IPv4 address
+    :type addr: str
+    :returns: Address string, optionally encapsulated in brackets([])
+    :rtype: str
+    :raises: ValueError
+    """
+    ipaddr = ipaddress.ip_address(addr)
+    if isinstance(ipaddr, ipaddress.IPv6Address):
+        fmt = '[{}]'
+    else:
+        fmt = '{}'
+    return fmt.format(ipaddr)
diff --git a/zaza/openstack/charm_tests/vault/utils.py b/zaza/openstack/charm_tests/vault/utils.py
index c05fcf6..a708d78 100644
--- a/zaza/openstack/charm_tests/vault/utils.py
+++ b/zaza/openstack/charm_tests/vault/utils.py
@@ -27,6 +27,7 @@ import yaml
 import collections
 
 import zaza.model
+import zaza.openstack.charm_tests.test_utils as test_utils
 
 AUTH_FILE = "vault_tests.yaml"
 CharmVaultClient = collections.namedtuple(
@@ -101,7 +102,7 @@ def get_unit_api_url(ip):
     transport = 'http'
     if vault_config['ssl-cert']['value']:
         transport = 'https'
-    return '{}://{}:8200'.format(transport, ip)
+    return '{}://{}:8200'.format(transport, test_utils.format_addr(ip))
 
 
 def get_hvac_client(vault_url, cacert=None):