--- a/thunderbird/mozillabuild.py
+++ b/thunderbird/mozillabuild.py
@@ -18,15 +18,15 @@ def setupHGPollersFromBranches(defaults,
         if hgurl[-1:] == '/':
             hgurl = hgurl[:-1]
         poll_branch = getConfig(defaults, branch, 'master_branch')
         for b in [poll_branch] + [getConfig(defaults, branch, 'mozilla_central_branch')] + getConfig(defaults, branch, 'add_poll_branches'):
             pushlogUrlOverride = '%s/%s/pushlog' % (hgurl, b),
             if not sources.get(b):
                 sources[b] = pushlogUrlOverride
 
-    for branch in sources.keys():
+    for branch in sorted(sources.keys()):
         change_source.append(HgPoller(
             hgURL=hgurl,
             pushlogUrlOverride="%s/%s/pushlog" % (hgurl,branch),
             branch=fixed_branch,
             pollInterval=1*60
         ))