diff -r 6509fcec830c -r ccf4d808ec4c mercurial/context.py
--- a/mercurial/context.py	Thu Oct 04 11:28:48 2018 +0200
+++ b/mercurial/context.py	Thu Oct 04 08:34:59 2018 +0200
@@ -734,6 +734,8 @@
         mfl = repo.manifestlog
         # fetch the linkrev
         lkr = self.linkrev()
+        if srcrev == lkr:
+            return lkr
         # hack to reuse ancestor computation when searching for renames
         memberanc = getattr(self, '_ancestrycontext', None)
         iteranc = None