--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -743,6 +743,8 @@ class revlog(object):
def lookup(self, id):
"""locate a node based on revision number or subset of hex nodeid"""
+ if id in self.nodemap:
+ return id
if type(id) == type(0):
rev = id
if rev < 0: rev = self.count() + rev