diff -r a48b3db0baba -r ea7588c11c36 mercurial/bundle2.py
--- a/mercurial/bundle2.py	Mon Sep 18 13:35:43 2017 -0400
+++ b/mercurial/bundle2.py	Mon Sep 18 13:36:05 2017 -0400
@@ -1019,7 +1019,8 @@
                 msg.append(')')
             if not self.data:
                 msg.append(' empty payload')
-            elif util.safehasattr(self.data, 'next'):
+            elif (util.safehasattr(self.data, 'next')
+                  or util.safehasattr(self.data, '__next__')):
                 msg.append(' streamed payload')
             else:
                 msg.append(' %i bytes payload' % len(self.data))