diff --git a/forwardport/models/project.py b/forwardport/models/project.py
index 3801b8b9..fe2d8ce9 100644
--- a/forwardport/models/project.py
+++ b/forwardport/models/project.py
@@ -906,18 +906,31 @@ stderr:
             new = configured.stdout().rev_parse('HEAD').stdout.decode()
             logger.info('%s: success -> %s', commit_sha, new)
 
+    def _build_merge_message(self, message, related_prs=()):
+        msg = super()._build_merge_message(message, related_prs=related_prs)
+
+        # ensures all reviewers in the review path are on the PR in order:
+        # original reviewer, then last conflict reviewer, then current PR
+        reviewers = (self | self._get_root() | self.source_id)\
+            .mapped('reviewed_by.formatted_email')
+
+        sobs = msg.headers.getlist('signed-off-by')
+        msg.headers.remove('signed-off-by')
+        msg.headers.extend(
+            ('signed-off-by', signer)
+            for signer in sobs
+            if signer not in reviewers
+        )
+        msg.headers.extend(
+            ('signed-off-by', reviewer)
+            for reviewer in reversed(reviewers)
+        )
+
+        return msg
+
     def _make_fp_message(self, commit):
         cmap = json.loads(self.commits_map)
         msg = self._parse_commit_message(commit['commit']['message'])
-        # original signed-off-er should be retained but didn't necessarily
-        # sign off here, so convert signed-off-by to something else
-        sob = msg.headers.getlist('signed-off-by')
-        if sob:
-            msg.headers.remove('signed-off-by')
-            msg.headers.extend(
-                ('original-signed-off-by', v)
-                for v in sob
-            )
         # write the *merged* commit as "original", not the PR's
         msg.headers['x-original-commit'] = cmap.get(commit['sha'], commit['sha'])
         # don't stringify so caller can still perform alterations
diff --git a/forwardport/tests/test_simple.py b/forwardport/tests/test_simple.py
index 61ed69e0..0c06b819 100644
--- a/forwardport/tests/test_simple.py
+++ b/forwardport/tests/test_simple.py
@@ -869,9 +869,23 @@ def test_access_rights(env, config, make_repo, users, author, reviewer, delegate
     if success:
         assert pr1.staging_id and pr2.staging_id,\
             "%s should have approved FP of PRs by %s" % (reviewer, author)
+        st = prod.commit('staging.b')
+        c = prod.commit(st.parents[0])
+        # Should be signed-off by both original reviewer and forward port reviewer
+        original_signoff = signoff(config['role_user'], c.message)
+        forward_signoff = signoff(config['role_' + reviewer], c.message)
+        assert c.message.index(original_signoff) <= c.message.index(forward_signoff),\
+            "Check that FP approver is after original PR approver as that's " \
+            "the review path for the PR"
     else:
         assert not (pr1.staging_id or pr2.staging_id),\
             "%s should *not* have approved FP of PRs by %s" % (reviewer, author)
+def signoff(conf, message):
+    for n in filter(None, [conf.get('name'), conf.get('user')]):
+        signoff = 'Signed-off-by: ' + n
+        if signoff in message:
+            return signoff
+    raise AssertionError("Failed to find signoff by %s in %s" % (conf, message))
 
 def test_batched(env, config, make_repo, users):
     """ Tests for projects with multiple repos & sync'd branches. Batches
diff --git a/runbot_merge/models/pull_requests.py b/runbot_merge/models/pull_requests.py
index d4407f18..00a4ea1a 100644
--- a/runbot_merge/models/pull_requests.py
+++ b/runbot_merge/models/pull_requests.py
@@ -1160,7 +1160,7 @@ class PullRequests(models.Model):
         if self.reviewed_by:
             m.headers.add('signed-off-by', self.reviewed_by.formatted_email)
 
-        return str(m)
+        return m
 
     def _stage(self, gh, target, related_prs=()):
         # nb: pr_commits is oldest to newest so pr.head is pr_commits[-1]
@@ -1190,7 +1190,7 @@ class PullRequests(models.Model):
         # updates head commit with PR number (if necessary) then rebases
         # on top of target
         msg = self._build_merge_message(commits[-1]['commit']['message'], related_prs=related_prs)
-        commits[-1]['commit']['message'] = msg
+        commits[-1]['commit']['message'] = str(msg)
         head, mapping = gh.rebase(self.number, target, commits=commits)
         self.commits_map = json.dumps({**mapping, '': head})
         return head
@@ -1198,7 +1198,7 @@ class PullRequests(models.Model):
     def _stage_rebase_merge(self, gh, target, commits, related_prs=()):
         msg = self._build_merge_message(self.message, related_prs=related_prs)
         h, mapping = gh.rebase(self.number, target, reset=True, commits=commits)
-        merge_head = gh.merge(h, target, msg)['sha']
+        merge_head = gh.merge(h, target, str(msg))['sha']
         self.commits_map = json.dumps({**mapping, '': merge_head})
         return merge_head
 
@@ -1224,7 +1224,7 @@ class PullRequests(models.Model):
             new_parents = [original_head] + list(head_parents - {base_commit})
             msg = self._build_merge_message(pr_head['commit']['message'], related_prs=related_prs)
             copy = gh('post', 'git/commits', json={
-                'message': msg,
+                'message': str(msg),
                 'tree': merge_tree,
                 'author': pr_head['commit']['author'],
                 'committer': pr_head['commit']['committer'],
@@ -1238,7 +1238,7 @@ class PullRequests(models.Model):
         else:
             # otherwise do a regular merge
             msg = self._build_merge_message(self.message)
-            merge_head = gh.merge(self.head, target, msg)['sha']
+            merge_head = gh.merge(self.head, target, str(msg))['sha']
             # and the merge commit is the normal merge head
             commits_map[''] = merge_head
             self.commits_map = json.dumps(commits_map)