diff --git a/runbot_merge/models/pull_requests.py b/runbot_merge/models/pull_requests.py
index 54755b10..9c012089 100644
--- a/runbot_merge/models/pull_requests.py
+++ b/runbot_merge/models/pull_requests.py
@@ -567,6 +567,8 @@ class PullRequests(models.Model):
                     if newstate:
                         self.state = newstate
                         ok = True
+                    else:
+                        msg = "This PR is already reviewed, reviewing it again is useless."
                 elif not param and is_author:
                     newstate = RMINUS.get(self.state)
                     if newstate:
diff --git a/runbot_merge/tests/test_basic.py b/runbot_merge/tests/test_basic.py
index 10a32f7d..3ffdf23d 100644
--- a/runbot_merge/tests/test_basic.py
+++ b/runbot_merge/tests/test_basic.py
@@ -1683,12 +1683,17 @@ class TestReviewing(object):
             ('repository.name', '=', repo.name),
             ('number', '=', prx.number)
         ]).state == 'ready'
+        # second r+ to check warning
+        prx.post_comment('hansen r+', user='reviewer')
 
         env['runbot_merge.project']._send_feedback()
         assert prx.comments == [
             (users['other'], 'hansen r+'),
             (users['reviewer'], 'hansen r+'),
+            (users['reviewer'], 'hansen r+'),
             (users['user'], "I'm sorry, @{}. I'm afraid I can't do that.".format(users['other'])),
+            (users['user'], "I'm sorry, @{}. This PR is already reviewed, reviewing it again is useless.".format(
+                 users['reviewer'])),
         ]
 
     def test_self_review_fail(self, env, repo, users):