mercurial/merge.py

--- a/mercurial/merge.py	Thu Jun 25 17:53:16 2015 -0500
+++ b/mercurial/merge.py	Thu Jun 25 17:54:55 2015 -0500
@@ -1011,7 +1011,7 @@
 
         p2 = repo[node]
         if pas[0] is None:
-            if repo.ui.config('merge', 'preferancestor', '*') == '*':
+            if repo.ui.configlist('merge', 'preferancestor', ['*']) == ['*']:
                 cahs = repo.changelog.commonancestorsheads(p1.node(), p2.node())
                 pas = [repo[anc] for anc in (sorted(cahs) or [nullid])]
             else: