diff --git a/master/buildbot/db/changes.py b/master/buildbot/db/changes.py
index 2fd996fb4fc..e54604f83b2 100644
--- a/master/buildbot/db/changes.py
+++ b/master/buildbot/db/changes.py
@@ -82,6 +82,9 @@ def addChange(self, who, files, comments, isdir=0, links=None,
 
         @returns: a L{buildbot.changes.changes.Change} instance via Deferred
         """
+        assert project is not None, "project must be a string, not None"
+        assert repository is not None, "repository must be a string, not None"
+
         # first create the change, although with no 'number'
         change = Change(who=who, files=files, comments=comments, isdir=isdir,
                 links=links, revision=revision, when=when, branch=branch,