diff -r 2e10ddbb9faa -r 68289ed170c7 mercurial/bundlerepo.py
--- a/mercurial/bundlerepo.py	Tue Feb 20 17:17:54 2024 +0100
+++ b/mercurial/bundlerepo.py	Tue Feb 20 17:18:15 2024 +0100
@@ -270,7 +270,7 @@
         raise NotImplementedError
 
     def _updateroots(self, phase, newroots, tr):
-        self.phaseroots[phase] = newroots
+        self._phaseroots[phase] = newroots
         self.invalidate()
         self.dirty = True