--- a/mercurial/phases.py	Sat Feb 17 11:19:52 2018 -0700
+++ b/mercurial/phases.py	Mon Feb 26 13:32:03 2018 -0800
@@ -326,7 +326,7 @@
 
     def _write(self, fp):
         for phase, roots in enumerate(self.phaseroots):
-            for h in roots:
+            for h in sorted(roots):
                 fp.write('%i %s\n' % (phase, hex(h)))
         self.dirty = False