diff -r 154298576d44 -r 967ac37f3d45 mercurial/scmutil.py
--- a/mercurial/scmutil.py	Sat Jul 08 16:50:31 2017 -0700
+++ b/mercurial/scmutil.py	Sun Jul 09 15:11:19 2017 +0200
@@ -638,7 +638,7 @@
             isobs = unfi.obsstore.successors.__contains__
             torev = unfi.changelog.rev
             sortfunc = lambda ns: torev(ns[0])
-            rels = [(unfi[n], (unfi[m] for m in s))
+            rels = [(unfi[n], tuple(unfi[m] for m in s))
                     for n, s in sorted(mapping.items(), key=sortfunc)
                     if s or not isobs(n)]
             obsolete.createmarkers(repo, rels, operation=operation)