diff --git a/devices.py b/devices.py
index 74e5bfa..3a334e7 100644
--- a/devices.py
+++ b/devices.py
@@ -584,8 +584,8 @@ class FrappyConfig(Device):
 
         predef_changes = []
         for aliasname, cfg in predef_aliases:
-            if cfg not in session.alias_config.get(aliasname, []):
-                predef_changes.append(cfg)
+            if cfg and cfg[0] not in session.alias_config.get(aliasname, []):
+                predef_changes.append((aliasname, cfg))
 
         return envlist, needed_aliases, predef_changes