diff --git a/mercurial/revlogutils/deltas.py b/mercurial/revlogutils/deltas.py
--- a/mercurial/revlogutils/deltas.py
+++ b/mercurial/revlogutils/deltas.py
@@ -1050,7 +1050,7 @@
             snapshotdepth,
         )
 
-    def finddeltainfo(self, revinfo, fh):
+    def finddeltainfo(self, revinfo, fh, excluded_base=None):
         """Find an acceptable delta against a candidate revision
 
         revinfo: information about the revision (instance of _revisioninfo)
@@ -1066,6 +1066,9 @@
         if not revinfo.textlen:
             return self._fullsnapshotinfo(fh, revinfo)
 
+        if excluded_base is None:
+            excluded_base = set()
+
         # no delta for flag processor revision (see "candelta" for why)
         # not calling candelta since only one revision needs test, also to
         # avoid overhead fetching flags again.
@@ -1090,6 +1093,8 @@
                 # challenge it against refined candidates
                 nominateddeltas.append(deltainfo)
             for candidaterev in candidaterevs:
+                if candidaterev in excluded_base:
+                    continue
                 candidatedelta = self._builddeltainfo(revinfo, candidaterev, fh)
                 if candidatedelta is not None:
                     if isgooddeltainfo(self.revlog, candidatedelta, revinfo):