--- a/mercurial/bundle2.py	Thu Mar 22 21:19:31 2018 +0900
+++ b/mercurial/bundle2.py	Thu Mar 22 21:56:20 2018 +0900
@@ -171,6 +171,9 @@
     url,
     util,
 )
+from .utils import (
+    stringutil,
+)
 
 urlerr = util.urlerr
 urlreq = util.urlreq
@@ -1091,7 +1094,7 @@
             ui.debug('bundle2-generatorexit\n')
             raise
         except BaseException as exc:
-            bexc = util.forcebytestr(exc)
+            bexc = stringutil.forcebytestr(exc)
             # backup exception data for later
             ui.debug('bundle2-input-stream-interrupt: encoding exception %s'
                      % bexc)