diff --git a/runbot_merge/models/pull_requests.py b/runbot_merge/models/pull_requests.py
index b03ef637..a6e62e02 100644
--- a/runbot_merge/models/pull_requests.py
+++ b/runbot_merge/models/pull_requests.py
@@ -1843,6 +1843,15 @@ class Stagings(models.Model):
                     self, prs
                 )
                 prs.write({'state': 'merged'})
+                pseudobranch = None
+                if self.target == project.branch_ids[:1] and project.branch_ids[1:2]:
+                    prev = project.branch_ids[1:2].name
+                    m = re.search(r'(\d+)(?:\.(\d+))?$', prev)
+                    if m:
+                        pseudobranch = "%s.%d" % (m[1], (int(m[2] or 0) + 1))
+                    else:
+                        pseudobranch = 'post-' + prev
+
                 for pr in prs:
                     self.env['runbot_merge.pull_requests.feedback'].create({
                         'repository': pr.repository.id,
@@ -1852,6 +1861,12 @@ class Stagings(models.Model):
                         }),
                         'close': True,
                     })
+                    if pseudobranch:
+                        self.env['runbot_merge.pull_requests.tagging'].create({
+                            'repository': pr.repository.id,
+                            'pull_request': pr.number,
+                            'tags_add': json.dumps([pseudobranch]),
+                        })
             finally:
                 self.batch_ids.write({'active': False})
                 self.write({'active': False})
diff --git a/runbot_merge/tests/test_by_branch.py b/runbot_merge/tests/test_by_branch.py
index 768ab293..ae635db3 100644
--- a/runbot_merge/tests/test_by_branch.py
+++ b/runbot_merge/tests/test_by_branch.py
@@ -111,3 +111,68 @@ def test_status_skipped(env, project, repo, config):
         repo.post_status('staging.maintenance', 'success', 'ci')
     env.run_crons('runbot_merge.process_updated_commits')
     assert st.state == 'success'
+
+def test_pseudo_version_tag(env, project, make_repo, setreviewers, config):
+    """ Because the last branch in the sequence is "live", if a PR's merged in
+    it it's hard to know where it landed in terms of other branches.
+
+    Therefore if a PR is merged in one such branch, tag it using the previous
+    branch of the sequence:
+
+    * if that ends with a number, increment the number by 1
+    * otherwise add 'post-' prefix (I guess)
+    """
+    repo = make_repo('repo')
+    project.branch_ids.sequence = 1
+    project.write({
+        'repo_ids': [(0, 0, {'name': repo.name, 'required_statuses': 'ci'})],
+        'branch_ids': [
+            (0, 0, {'name': '2.0', 'sequence': 11}),
+            (0, 0, {'name': '1.0', 'sequence': 21})
+        ],
+    })
+    setreviewers(*project.repo_ids)
+
+    with repo:
+        [m] = repo.make_commits(None, Commit('c1', tree={'a': '1'}), ref='heads/master')
+        repo.make_ref('heads/1.0', m)
+        repo.make_ref('heads/2.0', m)
+        repo.make_ref('heads/bonk', m)
+
+    with repo:
+        repo.make_commits(m, Commit('pr1', tree={'b': '1'}), ref='heads/change')
+        pr = repo.make_pr(target='master', head='change')
+        repo.post_status(pr.ref, 'success', 'ci')
+        pr.post_comment('hansen r+', config['role_reviewer']['token'])
+    env.run_crons() # should create staging
+    pr_id = env['runbot_merge.pull_requests'].search([
+        ('repository.name', '=', repo.name),
+        ('number', '=', pr.number)
+    ])
+    assert pr_id.state == 'ready'
+    assert pr_id.staging_id
+    with repo:
+        repo.post_status('staging.master', 'success', 'ci')
+    env.run_crons() # should merge staging
+    assert pr_id.state == 'merged'
+    assert pr.labels >= {'2.1'}
+
+    # now the second branch is non-numeric, therefore the label should just be prefixed by "post-"
+    project.write({'branch_ids': [(0, 0, {'name': 'bonk', 'sequence': 6})]})
+    with repo:
+        repo.make_commits(m, Commit('pr2', tree={'c': '1'}), ref='heads/change2')
+        pr = repo.make_pr(target='master', head='change2')
+        repo.post_status(pr.ref, 'success', 'ci')
+        pr.post_comment('hansen r+', config['role_reviewer']['token'])
+    env.run_crons() # should create staging
+    pr_id = env['runbot_merge.pull_requests'].search([
+        ('repository.name', '=', repo.name),
+        ('number', '=', pr.number)
+    ])
+    assert pr_id.state == 'ready', pr.comments
+    assert pr_id.staging_id
+    with repo:
+        repo.post_status('staging.master', 'success', 'ci')
+    env.run_crons() # should merge staging
+    assert pr_id.state == 'merged'
+    assert pr.labels >= {'post-bonk'}