diff --git a/resallocserver/manager.py b/resallocserver/manager.py
index f09b199..be711b9 100644
--- a/resallocserver/manager.py
+++ b/resallocserver/manager.py
@@ -157,7 +157,9 @@ def reload_config():
         assert not pool_id in pools
         pool = Pool(pool_id)
         pool.from_dict(config[pool_id])
-        if pool.tags and pool.tags_on_demand:
+        if pool.tags_on_demand:
+            if pool.tags is None:
+                pool.tags = []
             pool.tags += pool.tags_on_demand
             pool.max_prealloc = 0