diff --git a/mercurial/bundle2.py b/mercurial/bundle2.py
--- a/mercurial/bundle2.py
+++ b/mercurial/bundle2.py
@@ -859,9 +859,7 @@ class unbundle20(unpackermixin):
             # Ensure part is fully consumed so we can start reading the next
             # part.
             part.consume()
-            # But then seek back to the beginning so the code consuming this
-            # generator has a part that starts at 0.
-            part.seek(0, os.SEEK_SET)
+
             headerblock = self._readpartheader()
         indebug(self.ui, 'end of bundle2 stream')
 
diff --git a/mercurial/bundlerepo.py b/mercurial/bundlerepo.py
--- a/mercurial/bundlerepo.py
+++ b/mercurial/bundlerepo.py
@@ -288,18 +288,26 @@ class bundlerepository(localrepo.localre
             self._bundlefile = bundle
             self._cgunpacker = None
 
-            hadchangegroup = False
+            cgpart = None
             for part in bundle.iterparts():
                 if part.type == 'changegroup':
-                    if hadchangegroup:
+                    if cgpart:
                         raise NotImplementedError("can't process "
                                                   "multiple changegroups")
-                    hadchangegroup = True
+                    cgpart = part
 
                 self._handlebundle2part(bundle, part)
 
-            if not hadchangegroup:
+            if not cgpart:
                 raise error.Abort(_("No changegroups found"))
+
+            # This is required to placate a later consumer, which expects
+            # the payload offset to be at the beginning of the changegroup.
+            # We need to do this after the iterparts() generator advances
+            # because iterparts() will seek to end of payload after the
+            # generator returns control to iterparts().
+            cgpart.seek(0, os.SEEK_SET)
+
         elif isinstance(bundle, changegroup.cg1unpacker):
             if bundle.compressed():
                 f = self._writetempbundle(bundle.read, '.hg10un',