diff --git a/mercurial/bundle2.py b/mercurial/bundle2.py
--- a/mercurial/bundle2.py
+++ b/mercurial/bundle2.py
@@ -304,6 +304,7 @@ def _notransaction():
 
 def applybundle(repo, unbundler, tr, op=None):
     # transform me into unbundler.apply() as soon as the freeze is lifted
+    tr.hookargs['bundle2'] = '1'
     return processbundle(repo, unbundler, lambda: tr, op=op)
 
 def processbundle(repo, unbundler, transactiongetter=None, op=None):