diff -r 7415cc923613 -r 05d415790761 mercurial/debugcommands.py
--- a/mercurial/debugcommands.py	Fri Jan 19 00:18:45 2018 -0500
+++ b/mercurial/debugcommands.py	Thu Jan 18 16:47:14 2018 +0100
@@ -797,8 +797,8 @@
     [
         ('o', 'output', '', _('path')),
     ],
-    norepo=True)
-def debugdownload(ui, url, output=None, **opts):
+    optionalrepo=True)
+def debugdownload(ui, repo, url, output=None, **opts):
     """download a resource using Mercurial logic and config
     """
     fh = urlmod.open(ui, url, output)