diff --git a/runbot_merge/controllers.py b/runbot_merge/controllers.py
index bb6c8709..2835742c 100644
--- a/runbot_merge/controllers.py
+++ b/runbot_merge/controllers.py
@@ -142,8 +142,8 @@ def handle_pr(event):
                 pr_obj.staging_id,
             )
 
-        # TODO: should we update squash as well? What of explicit squash commands?
         pr_obj.head = pr['head']['sha']
+        pr_obj.squash = pr['commits'] == 1
         return 'Updated {} to {}'.format(pr_obj.id, pr_obj.head)
 
     # don't marked merged PRs as closed (!!!)
diff --git a/runbot_merge/models/pull_requests.py b/runbot_merge/models/pull_requests.py
index 57843e0c..920de9cd 100644
--- a/runbot_merge/models/pull_requests.py
+++ b/runbot_merge/models/pull_requests.py
@@ -833,8 +833,6 @@ class Batch(models.Model):
             msg = pr.message
             author=None
             if pr.squash:
-                # FIXME: maybe should be message of the *first* commit of the branch?
-                # TODO: or depend on # of commits in PR instead of squash flag?
                 commit = gh.commit(pr.head)
                 msg = commit['message']
                 author = commit['author']
diff --git a/runbot_merge/tests/test_basic.py b/runbot_merge/tests/test_basic.py
index 241cdb65..c95ebf41 100644
--- a/runbot_merge/tests/test_basic.py
+++ b/runbot_merge/tests/test_basic.py
@@ -536,6 +536,47 @@ class TestSquashing(object):
         ]).state == 'merged'
         assert prx.state == 'closed'
 
+    def test_pr_update_unsquash(self, repo, env):
+        """
+        If a PR starts with 1 commit and a second commit is added, the PR
+        should be unflagged as squash
+        """
+        m = repo.make_commit(None, 'initial', None, tree={'m': 'm'})
+        m2 = repo.make_commit(m, 'second', None, tree={'m': 'm', 'm2': 'm2'})
+        repo.make_ref('heads/master', m2)
+
+        c1 = repo.make_commit(m, 'first', None, tree={'m': 'c1'})
+        prx = repo.make_pr('title', 'body', target='master', ctid=c1, user='user')
+        pr = env['runbot_merge.pull_requests'].search([
+            ('repository.name', '=', 'odoo/odoo'),
+            ('number', '=', prx.number),
+        ])
+        assert pr.squash, "a PR with a single commit should be squashed"
+
+        prx.push(repo.make_commit(c1, 'second2', None, tree={'m': 'c2'}))
+        assert not pr.squash, "a PR with a single commit should not be squashed"
+
+    def test_pr_reset_squash(self, repo, env):
+        """
+        If a PR starts at >1 commits and is reset back to 1, the PR should be
+        re-flagged as squash
+        """
+        m = repo.make_commit(None, 'initial', None, tree={'m': 'm'})
+        m2 = repo.make_commit(m, 'second', None, tree={'m': 'm', 'm2': 'm2'})
+        repo.make_ref('heads/master', m2)
+
+        c1 = repo.make_commit(m, 'first', None, tree={'m': 'c1'})
+        c2 = repo.make_commit(c1, 'second2', None, tree={'m': 'c2'})
+        prx = repo.make_pr('title', 'body', target='master', ctid=c2, user='user')
+        pr = env['runbot_merge.pull_requests'].search([
+            ('repository.name', '=', 'odoo/odoo'),
+            ('number', '=', prx.number),
+        ])
+        assert not pr.squash, "a PR with a single commit should not be squashed"
+
+        prx.push(repo.make_commit(m, 'fixup', None, tree={'m': 'c2'}))
+        assert pr.squash, "a PR with a single commit should be squashed"
+
     @pytest.mark.xfail(reason="removed support for squash+ command")
     def test_force_squash_merge(self, repo, env):
         m = repo.make_commit(None, 'initial', None, tree={'m': 'm'})