diff -r cdf61ab1f54c -r 55db747a21ad mercurial/unionrepo.py
--- a/mercurial/unionrepo.py	Wed Oct 03 10:56:48 2018 -0700
+++ b/mercurial/unionrepo.py	Wed Oct 03 10:32:21 2018 -0700
@@ -110,7 +110,7 @@
 
         if rev > self.repotiprev:
             text = self.revlog2.revision(node)
-            self._cache = (node, rev, text)
+            self._revisioncache = (node, rev, text)
         else:
             text = self.baserevision(rev)
             # already cached