diff --git a/mercurial/obsolete.py b/mercurial/obsolete.py
--- a/mercurial/obsolete.py
+++ b/mercurial/obsolete.py
@@ -994,10 +994,10 @@ def _computephasedivergentset(repo):
     public = phases.public
     cl = repo.changelog
     torev = cl.nodemap.get
-    for ctx in repo.set('(not public()) and (not obsolete())'):
-        rev = ctx.rev()
+    tonode = cl.node
+    for rev in repo.revs('(not public()) and (not obsolete())'):
         # We only evaluate mutable, non-obsolete revision
-        node = ctx.node()
+        node = tonode(rev)
         # (future) A cache of predecessors may worth if split is very common
         for pnode in obsutil.allpredecessors(repo.obsstore, [node],
                                    ignoreflags=bumpedfix):