diff --git a/humbug/test_settings.py b/humbug/test_settings.py
index 78b4359f9d..973cab49f3 100644
--- a/humbug/test_settings.py
+++ b/humbug/test_settings.py
@@ -39,12 +39,9 @@ TUTORIAL_ENABLED = False
 # Disable use of memcached for caching
 CACHES = {
     'default': {
-        'BACKEND':  'django.core.cache.backends.dummy.DummyCache',
-        'LOCATION': 'humbug-default-test-cache',
-        'TIMEOUT':  3600,
-        'OPTIONS': {
-            'MAX_ENTRIES': 100000
-        },
+        'BACKEND':  'django.core.cache.backends.memcached.PyLibMCCache',
+        'LOCATION': '127.0.0.1:11211',
+        'TIMEOUT':  3600
     },
     'database': {
         'BACKEND':  'django.core.cache.backends.dummy.DummyCache',
diff --git a/zephyr/lib/cache.py b/zephyr/lib/cache.py
index f7c757f0a9..03bf2e7fc9 100644
--- a/zephyr/lib/cache.py
+++ b/zephyr/lib/cache.py
@@ -63,6 +63,10 @@ def get_or_create_key_prefix():
 
 KEY_PREFIX = get_or_create_key_prefix()
 
+def bounce_key_prefix_for_testing(test_name):
+    global KEY_PREFIX
+    KEY_PREFIX = test_name + ':' + str(os.getpid()) + ':'
+
 def get_cache_backend(cache_name):
     if cache_name is None:
         return djcache
diff --git a/zephyr/tests.py b/zephyr/tests.py
index 8682da702e..130b150a15 100644
--- a/zephyr/tests.py
+++ b/zephyr/tests.py
@@ -16,6 +16,7 @@ from zephyr.lib.actions import do_send_message, gather_subscriptions, \
     create_stream_if_needed, do_add_subscription
 from zephyr.lib.rate_limiter import add_ratelimit_rule, remove_ratelimit_rule
 from zephyr.lib import bugdown
+from zephyr.lib.cache import bounce_key_prefix_for_testing
 from zephyr.lib.rate_limiter import clear_user_history
 
 from django.conf import settings
@@ -1404,12 +1405,16 @@ so we didn't send them an invitation. We did send invitations to everyone else!"
         # We only sent emails to the new users.
         self.check_sent_emails(new)
 
-    @slow(0.35, 'inviting is slow')
-    def test_invite_outside_domain_in_open_realm(self):
+    @slow(0.20, 'inviting is slow')
+    def test_invite_outside_domain_in_closed_realm(self):
         """
-        In a realm with `restricted_to_domain = False`, you can invite people
+        In a realm with `restricted_to_domain = True`, you can't invite people
         with a different domain from that of the realm or your e-mail address.
         """
+        humbug_realm = Realm.objects.get(domain="humbughq.com")
+        humbug_realm.restricted_to_domain = True
+        humbug_realm.save()
+
         self.login("hamlet@humbughq.com")
         external_address = "foo@example.com"
 
@@ -1417,10 +1422,19 @@ so we didn't send them an invitation. We did send invitations to everyone else!"
             self.invite(external_address, ["Denmark"]),
             "Some emails did not validate, so we didn't send any invitations.")
 
+    @slow(0.20, 'inviting is slow')
+    def test_invite_outside_domain_in_open_realm(self):
+        """
+        In a realm with `restricted_to_domain = False`, you can invite people
+        with a different domain from that of the realm or your e-mail address.
+        """
         humbug_realm = Realm.objects.get(domain="humbughq.com")
         humbug_realm.restricted_to_domain = False
         humbug_realm.save()
 
+        self.login("hamlet@humbughq.com")
+        external_address = "foo@example.com"
+
         self.assert_json_success(self.invite(external_address, ["Denmark"]))
         self.check_sent_emails([external_address])
 
@@ -3008,6 +3022,9 @@ def run_test(test):
         return
 
     test_name = full_test_name(test)
+
+    bounce_key_prefix_for_testing(test_name)
+
     print 'Running %s' % (test_name,)
     test._pre_setup()