--- a/mercurial/phases.py	Mon May 21 17:33:50 2018 +0200
+++ b/mercurial/phases.py	Tue May 22 18:10:00 2018 +0200
@@ -126,6 +126,7 @@
 allphases = public, draft, secret = range(3)
 trackedphases = allphases[1:]
 phasenames = ['public', 'draft', 'secret']
+mutablephases = tuple(allphases[1:])
 
 def _readroots(repo, phasedefaults=None):
     """Read phase roots from disk