diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -2492,7 +2492,11 @@
     node1, node2 = ctx1.node(), ctx2.node()
 
     if reverse:
-        node1, node2 = node2, node1
+        ctxleft = ctx2
+        ctxright = ctx1
+    else:
+        ctxleft = ctx1
+        ctxright = ctx2
 
     diffopts = patch.diffallopts(ui, opts)
     m = scmutil.match(ctx2, pats, opts)
@@ -2502,8 +2506,8 @@
         ui,
         repo,
         diffopts,
-        repo[node1],
-        repo[node2],
+        ctxleft,
+        ctxright,
         m,
         stat=stat,
         listsubrepos=opts.get(b'subrepos'),