diff --git a/resallocserver/manager.py b/resallocserver/manager.py
index 36a8faf..8306c7b 100644
--- a/resallocserver/manager.py
+++ b/resallocserver/manager.py
@@ -688,6 +688,11 @@ def _clean_unknown_resources(self, event):
 
         with session_scope() as session:
             dbinfo = session.query(models.Pool).get(self.name)
+            if not dbinfo:
+                app.log.error("Can't perform cleanup in the configured "
+                              "pool %s: no such pool in database.",
+                              self.name)
+                return
             last_cleanup = dbinfo.cleaning_unknown_resources
             if last_cleanup is None:
                 last_cleanup = datetime.min