--- a/mercurial/fileset.py	Thu Jun 14 15:12:28 2018 -0700
+++ b/mercurial/fileset.py	Sat Jun 16 16:56:38 2018 +0900
@@ -427,7 +427,7 @@
     for f in mctx.existing():
         d = mctx.ctx[f].data()
         try:
-            d.decode(enc)
+            d.decode(pycompat.sysstr(enc))
         except LookupError:
             raise error.Abort(_("unknown encoding '%s'") % enc)
         except UnicodeDecodeError: