--- a/mercurial/changegroup.py
+++ b/mercurial/changegroup.py
@@ -50,7 +50,7 @@ class nocompress(object):
 bundletypes = {
     "": ("", nocompress),
     "HG10UN": ("HG10UN", nocompress),
-    "HG10BZ": ("HG10", lambda: bz2.BZ2Compressor(9)),
+    "HG10BZ": ("HG10", bz2.BZ2Compressor),
     "HG10GZ": ("HG10GZ", zlib.compressobj),
 }