diff -r b6eb56a9335d -r 457492741007 mercurial/bundle2.py
--- a/mercurial/bundle2.py	Wed May 28 15:53:34 2014 -0700
+++ b/mercurial/bundle2.py	Wed May 28 15:57:23 2014 -0700
@@ -831,8 +831,13 @@
 @parthandler('b2x:error:unsupportedcontent')
 def handlereplycaps(op, inpart):
     """Used to transmit unknown content error over the wire"""
-    parttype = inpart.params['parttype']
-    raise error.BundleValueError(parttype=parttype)
+    kwargs = {}
+    kwargs['parttype'] = inpart.params['parttype']
+    params = inpart.params.get('params')
+    if params is not None:
+        kwargs['params'] = params.split('\0')
+
+    raise error.BundleValueError(**kwargs)
 
 @parthandler('b2x:error:pushraced')
 def handlereplycaps(op, inpart):