diff --git a/mercurial/obsolete.py b/mercurial/obsolete.py
--- a/mercurial/obsolete.py
+++ b/mercurial/obsolete.py
@@ -939,7 +939,7 @@ def clearobscaches(repo):
 
 def _mutablerevs(repo):
     """the set of mutable revision in the repository"""
-    return repo._phasecache.getrevset(repo, phases.mutablephases)
+    return repo._phasecache.getrevset(repo, phases.relevant_mutable_phases)
 
 
 @cachefor(b'obsolete')
diff --git a/mercurial/phases.py b/mercurial/phases.py
--- a/mercurial/phases.py
+++ b/mercurial/phases.py
@@ -165,6 +165,7 @@ phasenumber2.update({phase: phase for ph
 phasenumber2.update({b'%i' % phase: phase for phase in phasenames})
 # record phase property
 mutablephases = (draft, secret, archived, internal)
+relevant_mutable_phases = (draft, secret)  # could be obsolete or unstable
 remotehiddenphases = (secret, archived, internal)
 localhiddenphases = (internal, archived)
 
diff --git a/tests/test-phases.t b/tests/test-phases.t
--- a/tests/test-phases.t
+++ b/tests/test-phases.t
@@ -1001,18 +1001,20 @@ Commit is hidden as expected
      summary:     A
   
 The hidden commit is an orphan but doesn't show up without --hidden
+And internal changesets are not considered for unstability.
 
   $ hg debugobsolete `hg id --debug -ir 0`
   1 new obsolescence markers
   obsoleted 1 changesets
-  $ hg --hidden log -G -r 'unstable()'
-  *  changeset:   1:c01c42dffc7f
+  $ hg --hidden log -G -r '(0::) - 0'
+  o  changeset:   1:c01c42dffc7f
   |  tag:         tip
   ~  user:        test
      date:        Thu Jan 01 00:00:00 1970 +0000
-     instability: orphan
      summary:     my test internal commit
   
+  $ hg --hidden log -G -r 'unstable()'
+
   $ hg log -G -r 'unstable()'