--- a/mercurial/revlog.py	Mon Mar 26 10:49:01 2018 -0700
+++ b/mercurial/revlog.py	Wed Mar 07 11:10:22 2018 +0100
@@ -345,6 +345,7 @@
                 # other approach failed try against prev to hopefully save us a
                 # fulltext.
                 yield (prev,)
+                tested.add(prev)
 
     def buildtext(self, revinfo, fh):
         """Builds a fulltext version of a revision