diff --git a/pupy/packages/posix/all/become.py b/pupy/packages/posix/all/become.py
index 08e6143d..9e56b3a5 100644
--- a/pupy/packages/posix/all/become.py
+++ b/pupy/packages/posix/all/become.py
@@ -49,7 +49,7 @@ def become(user):
 
     if os.path.exists(user_dbus_socket):
         os.environ['DBUS_SESSION_BUS_ADDRESS'] = 'unix:path='+user_dbus_socket
-    else:
+    elif 'DBUS_SESSION_BUS_ADDRESS' in os.environ:
         del os.environ['DBUS_SESSION_BUS_ADDRESS']
 
     for var in os.environ.keys():