diff --git a/mercurial/debugcommands.py b/mercurial/debugcommands.py
--- a/mercurial/debugcommands.py
+++ b/mercurial/debugcommands.py
@@ -2111,7 +2111,7 @@ def debugsuccessorssets(ui, repo, *revs)
     for rev in scmutil.revrange(repo, revs):
         ctx = repo[rev]
         ui.write('%s\n'% ctx2str(ctx))
-        for succsset in obsutil.successorssets(repo, ctx.node(), cache):
+        for succsset in obsutil.successorssets(repo, ctx.node(), cache=cache):
             if succsset:
                 ui.write('    ')
                 ui.write(node2str(succsset[0]))
diff --git a/mercurial/obsolete.py b/mercurial/obsolete.py
--- a/mercurial/obsolete.py
+++ b/mercurial/obsolete.py
@@ -958,7 +958,7 @@ def _computedivergentset(repo):
                 continue # emergency cycle hanging prevention
             seen.add(prec)
             if prec not in newermap:
-                obsutil.successorssets(repo, prec, newermap)
+                obsutil.successorssets(repo, prec, cache=newermap)
             newer = [n for n in newermap[prec] if n]
             if len(newer) > 1:
                 divergent.add(ctx.rev())