diff -r ce4ac5d19cb8 -r 3b4d69b3988d mercurial/hg.py
--- a/mercurial/hg.py	Mon Aug 01 06:08:25 2016 +0900
+++ b/mercurial/hg.py	Mon Aug 01 06:08:26 2016 +0900
@@ -896,7 +896,7 @@
                         ret = (ctx.sub(subpath, allowcreate=False).verify()
                                or ret)
                     except error.RepoError as e:
-                        repo.ui.warn(_('%s: %s\n') % (rev, e))
+                        repo.ui.warn(('%s: %s\n') % (rev, e))
             except Exception:
                 repo.ui.warn(_('.hgsubstate is corrupt in revision %s\n') %
                              node.short(ctx.node()))