diff --git a/conftest.py b/conftest.py
index b043a48b..b17d2b09 100644
--- a/conftest.py
+++ b/conftest.py
@@ -326,6 +326,7 @@ class DbDict(dict):
             f.write(db)
             f.flush()
             os.fsync(f.fileno())
+            subprocess.run(['psql', db, '-c', "UPDATE ir_cron SET nextcall = 'infinity'"])
 
         return db
 
diff --git a/runbot_merge/models/crons/cleanup_scratch_branches.py b/runbot_merge/models/crons/cleanup_scratch_branches.py
index a5e041ce..cfe05f32 100644
--- a/runbot_merge/models/crons/cleanup_scratch_branches.py
+++ b/runbot_merge/models/crons/cleanup_scratch_branches.py
@@ -9,10 +9,11 @@ class BranchCleanup(models.TransientModel):
     _description = "cleans up scratch refs for deactivated branches"
 
     def _run(self):
-        deactivated = self.env['runbot_merge.branch'].search([
-            ('active', '=', False),
-            ('write_date', '>=', self.env.context['lastcall']),
-        ])
+        domain = [('active', '=', False)]
+        if lastcall := self.env.context['lastcall']:
+            domain.append(('write_date', '>=', lastcall))
+        deactivated = self.env['runbot_merge.branch'].search(domain)
+
         _logger.info(
             "deleting scratch (tmp and staging) refs for branches %s",
             ', '.join(b.name for b in deactivated)