mercurial/phases.py

--- a/mercurial/phases.py	Sat Aug 08 10:06:32 2020 -0700
+++ b/mercurial/phases.py	Fri Aug 07 18:01:48 2020 +0530
@@ -125,6 +125,7 @@
     txnutil,
     util,
 )
+from .interfaces import repository
 
 _fphasesentry = struct.Struct(b'>i20s')
 
@@ -154,7 +155,7 @@
 
 def supportinternal(repo):
     """True if the internal phase can be used on a repository"""
-    return b'internal-phase' in repo.requirements
+    return repository.INTERNAL_PHASE_REQUIREMENT in repo.requirements
 
 
 def _readroots(repo, phasedefaults=None):