--- a/mercurial/commands.py	Wed Sep 19 17:09:01 2018 +0200
+++ b/mercurial/commands.py	Sat Sep 15 11:50:07 2018 +0900
@@ -1011,7 +1011,9 @@
             return 1
         ui.write("%s\n" % book, label=bookmarks.activebookmarklabel)
     else: # show bookmarks
-        bookmarks.printbookmarks(ui, repo, **opts)
+        opts = pycompat.byteskwargs(opts)
+        with ui.formatter('bookmarks', opts) as fm:
+            bookmarks.printbookmarks(ui, repo, fm)
 
 @command('branch',
     [('f', 'force', None,