diff -r 4b93e19cd6e6 -r c1ceec0c8cb4 mercurial/patch.py
--- a/mercurial/patch.py	Wed Jul 02 00:01:13 2014 -0500
+++ b/mercurial/patch.py	Wed Aug 14 13:10:27 2013 -0500
@@ -1622,7 +1622,7 @@
 
     revs = None
     hexfunc = repo.ui.debugflag and hex or short
-    revs = [hexfunc(node) for node in [node1, node2] if node]
+    revs = [hexfunc(node) for node in [ctx1.node(), ctx2.node()] if node]
 
     copy = {}
     if opts.git or opts.upgrade: