diff -r f206543d8380 -r 127b59787fd5 mercurial/util.py
--- a/mercurial/util.py	Sat Sep 26 17:24:12 2015 +0800
+++ b/mercurial/util.py	Wed Sep 23 11:33:30 2015 -0700
@@ -2378,7 +2378,8 @@
     return d
 
 decompressors = {None: lambda fh: fh,
-                 'BZ': _makedecompressor(_bz2),
+                 '_truncatedBZ': _makedecompressor(_bz2),
+                 'BZ': _makedecompressor(lambda: bz2.BZ2Decompressor()),
                  'GZ': _makedecompressor(lambda: zlib.decompressobj()),
                  }
 # also support the old form by courtesies