diff -r 07bcbf326c8d -r 1ff06386217f mercurial/exchange.py
--- a/mercurial/exchange.py	Wed Apr 16 18:41:48 2014 -0400
+++ b/mercurial/exchange.py	Wed Apr 16 14:09:35 2014 -0400
@@ -208,6 +208,7 @@
     evolve in the future."""
     # Send known head to the server for race detection.
     bundler = bundle2.bundle20(pushop.ui)
+    bundler.addpart(bundle2.bundlepart('replycaps'))
     if not pushop.force:
         part = bundle2.bundlepart('CHECK:HEADS', data=iter(pushop.remoteheads))
         bundler.addpart(part)