diff --git a/src/calibre/test_build.py b/src/calibre/test_build.py
index df87cef400..143f24389e 100644
--- a/src/calibre/test_build.py
+++ b/src/calibre/test_build.py
@@ -32,12 +32,14 @@ class BuildTest(unittest.TestCase):
     @unittest.skipUnless(islinux, 'DBUS only used on linux')
     def test_dbus(self):
         import dbus
+        bus = None
         if 'DISPLAY' in os.environ:
             bus = dbus.SystemBus()
             self.assertTrue(bus.list_names(), 'Failed to list names on the system bus')
+        if 'DBUS_SESSION_BUS_ADDRESS' in os.environ:
             bus = dbus.SessionBus()
             self.assertTrue(bus.list_names(), 'Failed to list names on the session bus')
-            del bus
+        del bus
 
     def test_regex(self):
         import regex