diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -708,9 +708,6 @@ class revlog(object):
         a, b = self.rev(a), self.rev(b)
         try:
             ancs = self.index.ancestors(a, b)
-            old = ancestor.ancestors(self.parentrevs, a, b)
-            assert set(ancs) == old, ('opinions differ over ancestor(%d, %d)' %
-                                      (a, b))
         except (AttributeError, OverflowError):
             ancs = ancestor.ancestors(self.parentrevs, a, b)
         if ancs: