--- a/mercurial/revlog.py	Sat Jun 30 16:06:05 2018 -0700
+++ b/mercurial/revlog.py	Thu Jun 21 23:53:43 2018 +0100
@@ -1378,6 +1378,8 @@
     def descendant(self, start, end):
         if start == nullrev:
             return True
+        elif start == end:
+            return True
         for i in self.descendants([start]):
             if i == end:
                 return True