--- a/hgext/evolve.py
+++ b/hgext/evolve.py
@@ -2154,14 +2154,14 @@
     if len(roots) > 1:
         raise util.Abort(_("cannot fold non-linear revisions "
                            "(multiple roots given)"))
-    root = repo[roots[0]]
+    root = repo[roots.first()]
     if root.phase() <= phases.public:
         raise util.Abort(_("cannot fold public revisions"))
     heads = repo.revs('heads(%ld)', revs)
     if len(heads) > 1:
         raise util.Abort(_("cannot fold non-linear revisions "
                            "(multiple heads given)"))
-    head = repo[heads[0]]
+    head = repo[heads.first()]
     wlock = lock = None
     try:
         wlock = repo.wlock()