diff --git a/src/calng/stacking_utils.py b/src/calng/stacking_utils.py
index 9613858860c3983a372e59ec2cf20494b9701a4d..b6d21a3d6d99a990acc82af28c7ea9735605c470 100644
--- a/src/calng/stacking_utils.py
+++ b/src/calng/stacking_utils.py
@@ -8,6 +8,7 @@ from karabo.bound import (
     TABLE_ELEMENT,
     Hash,
     Schema,
+    State,
 )
 import numpy as np
 
@@ -87,7 +88,7 @@ class StackingFriend:
     @staticmethod
     def add_schema(self, schema):
         (
-            TABLE_ELEMENT(expected)
+            TABLE_ELEMENT(schema)
             .key("merge")
             .displayedName("Array stacking")
             .allowedStates(State.PASSIVE)