diff -r af4158b8876b -r ffddabb8aa5d mercurial/localrepo.py
--- a/mercurial/localrepo.py	Mon Apr 07 11:45:50 2014 -0700
+++ b/mercurial/localrepo.py	Tue Apr 08 13:05:29 2014 -0700
@@ -281,7 +281,7 @@
         # required by the tests (or some brave tester)
         if not self.ui.configbool('server', 'bundle2', False):
             caps = set(caps)
-            caps.remove('bundle2')
+            caps.discard('bundle2')
         return caps
 
     def _applyrequirements(self, requirements):