--- a/mercurial/bundle2.py	Thu Aug 03 20:08:31 2017 -0700
+++ b/mercurial/bundle2.py	Thu Aug 03 23:02:32 2017 +0900
@@ -1045,7 +1045,7 @@
             ui.debug('bundle2-generatorexit\n')
             raise
         except BaseException as exc:
-            bexc = pycompat.bytestr(exc)
+            bexc = util.forcebytestr(exc)
             # backup exception data for later
             ui.debug('bundle2-input-stream-interrupt: encoding exception %s'
                      % bexc)