diff --git a/master/buildbot/test/fake/fakemaster.py b/master/buildbot/test/fake/fakemaster.py
index <HASH>..<HASH> 100644
--- a/master/buildbot/test/fake/fakemaster.py
+++ b/master/buildbot/test/fake/fakemaster.py
@@ -170,7 +170,7 @@ class FakeMaster(service.MasterService):
         service.MasterService.__init__(self)
         self._master_id = master_id
         self.reactor = reactor
-        self.objectids = []
+        self.objectids = {}
         self.config = config.MasterConfig()
         self.caches = FakeCaches()
         self.pbmanager = pbmanager.FakePBManager()
pylint: fix potential error