diff -r 230489fc0b41 -r b44a47214122 mercurial/commands.py
--- a/mercurial/commands.py	Sun Feb 11 16:16:43 2018 -0800
+++ b/mercurial/commands.py	Sun Feb 11 16:21:30 2018 -0800
@@ -1551,7 +1551,7 @@
 
     extra = {}
     if opts.get('close_branch'):
-        extra['close'] = 1
+        extra['close'] = '1'
 
         if not bheads:
             raise error.Abort(_('can only close branch heads'))