diff --git a/mercurial/bundle2.py b/mercurial/bundle2.py
--- a/mercurial/bundle2.py
+++ b/mercurial/bundle2.py
@@ -521,6 +521,10 @@ class unpackermixin(object):
         if util.safehasattr(self._fp, 'close'):
             return self._fp.close()
 
+def getunbundler(ui, fp, header=None):
+    """return a valid unbundler object for a given header"""
+    return unbundle20(ui, fp, header)
+
 class unbundle20(unpackermixin):
     """interpret a bundle2 stream
 
diff --git a/mercurial/exchange.py b/mercurial/exchange.py
--- a/mercurial/exchange.py
+++ b/mercurial/exchange.py
@@ -33,7 +33,7 @@ def readbundle(ui, fh, fname, vfs=None):
             alg = changegroup.readexactly(fh, 2)
         return changegroup.cg1unpacker(fh, alg)
     elif version == '2Y':
-        return bundle2.unbundle20(ui, fh, header=magic + version)
+        return bundle2.getunbundler(ui, fh, header=magic + version)
     else:
         raise util.Abort(_('%s: unknown bundle version %s') % (fname, version))
 
diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -114,7 +114,7 @@ class localpeer(peer.peerrepository):
             # When requesting a bundle2, getbundle returns a stream to make the
             # wire level function happier. We need to build a proper object
             # from it in local peer.
-            cg = bundle2.unbundle20(self.ui, cg)
+            cg = bundle2.getunbundler(self.ui, cg)
         return cg
 
     # TODO We might want to move the next two calls into legacypeer and add
@@ -132,7 +132,7 @@ class localpeer(peer.peerrepository):
                 # This little dance should be dropped eventually when the API
                 # is finally improved.
                 stream = util.chunkbuffer(ret.getchunks())
-                ret = bundle2.unbundle20(self.ui, stream)
+                ret = bundle2.getunbundler(self.ui, stream)
             return ret
         except error.PushRaced, exc:
             raise error.ResponseError(_('push failed:'), str(exc))
diff --git a/mercurial/wireproto.py b/mercurial/wireproto.py
--- a/mercurial/wireproto.py
+++ b/mercurial/wireproto.py
@@ -364,7 +364,7 @@ class wirepeer(peer.peerrepository):
         f = self._callcompressable("getbundle", **opts)
         bundlecaps = kwargs.get('bundlecaps')
         if bundlecaps is not None and 'HG2Y' in bundlecaps:
-            return bundle2.unbundle20(self.ui, f)
+            return bundle2.getunbundler(self.ui, f)
         else:
             return changegroupmod.cg1unpacker(f, 'UN')
 
@@ -401,7 +401,7 @@ class wirepeer(peer.peerrepository):
         else:
             # bundle2 push. Send a stream, fetch a stream.
             stream = self._calltwowaystream('unbundle', cg, heads=heads)
-            ret = bundle2.unbundle20(self.ui, stream)
+            ret = bundle2.getunbundler(self.ui, stream)
         return ret
 
     def debugwireargs(self, one, two, three=None, four=None, five=None):
diff --git a/tests/test-bundle2-format.t b/tests/test-bundle2-format.t
--- a/tests/test-bundle2-format.t
+++ b/tests/test-bundle2-format.t
@@ -157,7 +157,7 @@ Create an extension to test bundle2 API
   >         lock = repo.lock()
   >         tr = repo.transaction('processbundle')
   >         try:
-  >             unbundler = bundle2.unbundle20(ui, sys.stdin)
+  >             unbundler = bundle2.getunbundler(ui, sys.stdin)
   >             op = bundle2.processbundle(repo, unbundler, lambda: tr)
   >             tr.close()
   >         except error.BundleValueError, exc:
@@ -183,7 +183,7 @@ Create an extension to test bundle2 API
   > @command('statbundle2', [], '')
   > def cmdstatbundle2(ui, repo):
   >     """print statistic on the bundle2 container read from stdin"""
-  >     unbundler = bundle2.unbundle20(ui, sys.stdin)
+  >     unbundler = bundle2.getunbundler(ui, sys.stdin)
   >     try:
   >         params = unbundler.params
   >     except error.BundleValueError, exc: