diff --git a/mercurial/revlogutils/deltas.py b/mercurial/revlogutils/deltas.py
--- a/mercurial/revlogutils/deltas.py
+++ b/mercurial/revlogutils/deltas.py
@@ -596,8 +596,8 @@ def _candidategroups(revlog, textlen, p1
         for rev in temptative:
             # skip over empty delta (no need to include them in a chain)
             while not (rev == nullrev or rev in tested or deltalength(rev)):
+                tested.add(rev)
                 rev = deltaparent(rev)
-                tested.add(rev)
             # filter out revision we tested already
             if rev in tested:
                 continue