diff --git a/goodwe_controller/test_safety129.py b/goodwe_controller/test_safety129.py
index 7ef4a23..11c1c45 100644
--- a/goodwe_controller/test_safety129.py
+++ b/goodwe_controller/test_safety129.py
@@ -205,7 +205,7 @@ def fed(values):
     a.meter.slow = lambda: True
     a.meter.estimate = a.delay.estimate = lambda: None
     it = iter(values)
-    a.meter_slow.estimate = lambda: next(it)
+    a.meter_slow.estimate = lambda: next(it, None)
     for k in range(len(values)):
         a.watch(2.0 * k, [], 0.0, 0.0)
     return a