--- a/mercurial/store.py	Wed Dec 26 13:44:37 2018 +0100
+++ b/mercurial/store.py	Wed Jan 02 10:29:12 2019 +0100
@@ -523,7 +523,7 @@
             self._load()
         return iter(self.entries | self.addls)
 
-class _fncachevfs(vfsmod.abstractvfs, vfsmod.proxyvfs):
+class _fncachevfs(vfsmod.proxyvfs):
     def __init__(self, vfs, fnc, encode):
         vfsmod.proxyvfs.__init__(self, vfs)
         self.fncache = fnc