diff --git a/remotefilelog/shallowbundle.py b/remotefilelog/shallowbundle.py
--- a/remotefilelog/shallowbundle.py
+++ b/remotefilelog/shallowbundle.py
@@ -58,8 +58,15 @@
 
     return True
 
-@shallowutil.interposeclass(changegroup, 'cg1packer')
-class shallowcg1packer(changegroup.cg1packer):
+if util.safehasattr(changegroup, 'cg1packer'):
+    # Up until 4c99c6d1ef95
+    cgpacker = changegroup.cg1packer
+else:
+    # Since 4c99c6d1ef95
+    cgpacker = changegroup.cgpacker
+
+@shallowutil.interposeclass(changegroup, cgpacker.__name__)
+class shallowcg1packer(cgpacker):
     def generate(self, commonrevs, clnodes, fastpathlinkrev, source):
         if "remotefilelog" in self._repo.requirements:
             fastpathlinkrev = False
@@ -226,8 +233,14 @@
 
 if util.safehasattr(changegroup, 'cg2packer'):
     # Mercurial >= 3.3
-    @shallowutil.interposeclass(changegroup, 'cg2packer')
-    class shallowcg2packer(changegroup.cg2packer):
+    cg2packer = changegroup.cg2packer
+elif util.safehasattr(changegroup, 'cgpacker'):
+    # Since Mercurial 4c99c6d1ef95
+    cg2packer = changegroup.cgpacker
+
+if cg2packer:
+    @shallowutil.interposeclass(changegroup, cg2packer.__name__)
+    class shallowcg2packer(cg2packer):
         def group(self, nodelist, rlog, lookup, units=None, reorder=None):
             # for revlogs, shallowgroup will be called twice in the same stack
             # -- once here, once up the inheritance hierarchy in
@@ -239,8 +252,14 @@
                                 units=units)
 
 if util.safehasattr(changegroup, 'cg3packer'):
-    @shallowutil.interposeclass(changegroup, 'cg3packer')
-    class shallowcg3packer(changegroup.cg3packer):
+    cg3packer = changegroup.cg3packer
+elif util.safehasattr(changegroup, 'cgpacker'):
+    # Since Mercurial 4c99c6d1ef95
+    cg3packer = changegroup.cgpacker
+
+if cgpacker:
+    @shallowutil.interposeclass(changegroup, cg3packer.__name__)
+    class shallowcg3packer(cg3packer):
         def generatemanifests(self, commonrevs, clrevorder, fastpathlinkrev,
                               mfs, fnodes, *args, **kwargs):
             chunks = super(shallowcg3packer, self).generatemanifests(