--- a/mercurial/patch.py
+++ b/mercurial/patch.py
@@ -516,7 +516,7 @@ def diff(repo, node1=None, node2=None, f
src = repo.dirstate.copied(f)
parent = repo.dirstate.parents()[0]
if src:
- f = src[0]
+ f = src
of = renamedbetween(f, node1, parent)
if of:
return of