diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -2455,7 +2455,7 @@
 @command(
     b'diff',
     [
-        (b'r', b'rev', [], _(b'revision'), _(b'REV')),
+        (b'r', b'rev', [], _(b'revision (DEPRECATED)'), _(b'REV')),
         (b'', b'from', b'', _(b'revision to diff from'), _(b'REV1')),
         (b'', b'to', b'', _(b'revision to diff to'), _(b'REV2')),
         (b'c', b'change', b'', _(b'change made by revision'), _(b'REV')),
diff --git a/relnotes/next b/relnotes/next
--- a/relnotes/next
+++ b/relnotes/next
@@ -21,7 +21,8 @@
    debugstrip`. The extension remains for compatibility.
 
  * `hg diff` now supports `--from <rev>` and `--to <rev>` arguments as
-   clearer alternatives to `-r <revs>`.
+   clearer alternatives to `-r <revs>`. `-r <revs>` has been
+   deprecated.
 
  * The memory footprint per changeset during pull/unbundle
    operations has been further reduced.
diff --git a/tests/test-help.t b/tests/test-help.t
--- a/tests/test-help.t
+++ b/tests/test-help.t
@@ -665,7 +665,6 @@
   
   options ([+] can be repeated):
   
-   -r --rev REV [+]         revision
       --from REV1           revision to diff from
       --to REV2             revision to diff to
    -c --change REV          change made by revision