diff --git a/test/resources/qaoa_utils.py b/test/resources/qaoa_utils.py
index 303f9e3..81cd374 100644
--- a/test/resources/qaoa_utils.py
+++ b/test/resources/qaoa_utils.py
@@ -90,7 +90,7 @@ def tf_cost():
             _cached_cost_before = cost_function(params)
             return _cached_cost_before
 
-        optimizer.apply([tf_cost], [params])
+        optimizer.apply(tf_cost, [params])
         cost_before = _cached_cost_before
 
         # Alternative: