diff --git a/hgext/notify.py b/hgext/notify.py
--- a/hgext/notify.py
+++ b/hgext/notify.py
@@ -238,7 +238,7 @@ class notifier(object):
             return
         fp = templater.stringio()
         prev = self.repo.changelog.parents(node)[0]
-        patch.diff(self.repo, fp, prev, ref)
+        patch.diff(self.repo, prev, ref, fp=fp)
         difflines = fp.getvalue().splitlines(1)
         if maxdiff > 0 and len(difflines) > maxdiff:
             self.sio.write(_('\ndiffs (truncated from %d to %d lines):\n\n') %