diff --git a/mercurial/httprepo.py b/mercurial/httprepo.py
--- a/mercurial/httprepo.py
+++ b/mercurial/httprepo.py
@@ -354,6 +354,7 @@ class httprepository(remoterepository):
             fp.close()
 
     def lookup(self, key):
+        self.requirecap('lookup', _('look up remote revision'))
         d = self.do_cmd("lookup", key = key).read()
         success, data = d[:-1].split(' ', 1)
         if int(success):
@@ -391,6 +392,7 @@ class httprepository(remoterepository):
         return util.chunkbuffer(zgenerator(f))
 
     def changegroupsubset(self, bases, heads, source):
+        self.requirecap('changegroupsubset', _('look up remote changes'))
         baselst = " ".join([hex(n) for n in bases])
         headlst = " ".join([hex(n) for n in heads])
         f = self.do_cmd("changegroupsubset", bases=baselst, heads=headlst)