diff --git a/sugar/datastore/dbus_helpers.py b/sugar/datastore/dbus_helpers.py
index 3116e618..6680cc12 100644
--- a/sugar/datastore/dbus_helpers.py
+++ b/sugar/datastore/dbus_helpers.py
@@ -77,5 +77,5 @@ def mounts():
     return _data_store.mounts()
 
 def get_unique_values(key):
-    return _data_store.get_uniquevaluesfor(key, {})
+    return _data_store.get_uniquevaluesfor(key, dbus.Dictionary({}, signature='ss'))