diff --git a/conftest.py b/conftest.py
index 20678ef3..72e62618 100644
--- a/conftest.py
+++ b/conftest.py
@@ -783,7 +783,8 @@ class Repo:
     def post_status(self, ref, status, context='default', **kw):
         assert self.hook
         assert status in ('error', 'failure', 'pending', 'success')
-        r = self._session.post('https://api.github.com/repos/{}/statuses/{}'.format(self.name, self.commit(ref).id), json={
+        commit = ref if isinstance(ref, Commit) else self.commit(ref)
+        r = self._session.post('https://api.github.com/repos/{}/statuses/{}'.format(self.name, commit.id), json={
             'state': status,
             'context': context,
             **kw
diff --git a/runbot_merge/changelog/2022-10/statuses.md b/runbot_merge/changelog/2022-10/statuses.md
new file mode 100644
index 00000000..0cc418c7
--- /dev/null
+++ b/runbot_merge/changelog/2022-10/statuses.md
@@ -0,0 +1,10 @@
+FIX: lock in statuses at the end of a staging
+
+The statuses of a staging are computed dynamically. Because github associates
+statuses with *commits*, rebuilding a staging (partially or completely) or using
+one of its commits for a branch could lead to the statuses becoming inconsistent
+with the staging e.g. all-green statuses while the staging had failed.
+
+By locking in the status at the end of the staging, the dashboard is less 
+confusing and more consistent, and post-mortem analysis (e.g. of staging
+failures) easier.
diff --git a/runbot_merge/models/pull_requests.py b/runbot_merge/models/pull_requests.py
index 0cedc5fc..8134ea65 100644
--- a/runbot_merge/models/pull_requests.py
+++ b/runbot_merge/models/pull_requests.py
@@ -1714,6 +1714,25 @@ class Stagings(models.Model):
     head_ids = fields.Many2many('runbot_merge.commit', compute='_compute_statuses')
 
     statuses = fields.Binary(compute='_compute_statuses')
+    statuses_cache = fields.Text()
+
+    def write(self, vals):
+        # don't allow updating the statuses_cache
+        vals.pop('statuses_cache', None)
+
+        if 'state' not in vals:
+            return super().write(vals)
+
+        previously_pending = self.filtered(lambda s: s.state == 'pending')
+        super(Stagings, self).write(vals)
+        for staging in previously_pending:
+            if staging.state != 'pending':
+                super(Stagings, staging).write({
+                    'statuses_cache': json.dumps(staging.statuses)
+                })
+
+        return True
+
 
     def name_get(self):
         return [
@@ -1738,6 +1757,10 @@ class Stagings(models.Model):
                 if not repo.endswith('^')
             }
             commits = st.head_ids = Commits.search([('sha', 'in', list(heads.keys()))])
+            if st.statuses_cache:
+                st.statuses = json.loads(st.statuses_cache)
+                continue
+
             st.statuses = [
                 (
                     heads[commit.sha],
diff --git a/runbot_merge/tests/test_oddities.py b/runbot_merge/tests/test_oddities.py
index 3ad1289b..cdce2db0 100644
--- a/runbot_merge/tests/test_oddities.py
+++ b/runbot_merge/tests/test_oddities.py
@@ -1,6 +1,6 @@
 import requests
 
-from utils import Commit, to_pr
+from utils import Commit, to_pr, seen
 
 
 def test_partner_merge(env):
@@ -129,3 +129,51 @@ def test_unreviewer(env, project, port):
     assert 'error' not in r.json()
 
     assert p.review_rights == env['res.partner.review']
+
+def test_staging_post_update(env, project, make_repo, setreviewers, users, config):
+    """Because statuses come from commits, it's possible to update the commits
+    of a staging after that staging has completed (one way or the other), either
+    by sending statuses directly (e.g. rebuilding, for non-deterministic errors)
+    or just using the staging's head commit in a branch.
+
+    This makes post-mortem analysis quite confusing, so stagings should
+    "lock in" their statuses once they complete.
+    """
+    repo = make_repo('repo')
+    project.write({'repo_ids': [(0, 0, {
+        'name': repo.name,
+        'group_id': False,
+        'required_statuses': 'legal/cla,ci/runbot'
+    })]})
+    setreviewers(*project.repo_ids)
+
+    with repo:
+        [m] = repo.make_commits(None, Commit('initial', tree={'m': 'm'}), ref='heads/master')
+
+        repo.make_commits(m, Commit('thing', tree={'m': 'c'}), ref='heads/other')
+        pr = repo.make_pr(target='master', head='other')
+        repo.post_status(pr.head, 'success', 'ci/runbot')
+        repo.post_status(pr.head, 'success', 'legal/cla')
+        pr.post_comment('hansen r+ rebase-merge', config['role_reviewer']['token'])
+    env.run_crons()
+    pr_id = to_pr(env, pr)
+    staging_id = pr_id.staging_id
+    assert staging_id
+
+    staging_head = repo.commit('staging.master')
+    with repo:
+        repo.post_status(staging_head, 'failure', 'ci/runbot')
+    env.run_crons()
+    assert pr_id.state == 'error'
+    assert staging_id.state == 'failure'
+    assert staging_id.statuses == [
+        [repo.name, 'ci/runbot', 'failure', ''],
+    ]
+
+    with repo:
+        repo.post_status(staging_head, 'success', 'ci/runbot')
+    env.run_crons()
+    assert staging_id.state == 'failure'
+    assert staging_id.statuses == [
+        [repo.name, 'ci/runbot', 'failure', ''],
+    ]