diff -r 4fe63b573791 -r c7618901584d mercurial/obsutil.py
--- a/mercurial/obsutil.py	Fri Nov 02 14:24:29 2018 -0400
+++ b/mercurial/obsutil.py	Fri Oct 19 00:53:18 2018 +0200
@@ -148,10 +148,11 @@
 
     remaining = set(nodes)
     seen = set(remaining)
+    prec = obsstore.predecessors.get
     while remaining:
         current = remaining.pop()
         yield current
-        for mark in obsstore.predecessors.get(current, ()):
+        for mark in prec(current, ()):
             # ignore marker flagged with specified flag
             if mark[2] & ignoreflags:
                 continue