--- a/mercurial/revlogutils/deltas.py	Wed Sep 12 23:10:59 2018 -0400
+++ b/mercurial/revlogutils/deltas.py	Mon Sep 10 10:11:21 2018 +0200
@@ -596,8 +596,8 @@
         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