diff --git a/Trigger/TrigValidation/TrigValTools/bin/trigvalsteering-unit-tester.py b/Trigger/TrigValidation/TrigValTools/bin/trigvalsteering-unit-tester.py
index e8efbfae724a3652f57659ea57fd089753756ba3..6e49a502e02594cdaa3799db56ce91a53c2c3a53 100755
--- a/Trigger/TrigValidation/TrigValTools/bin/trigvalsteering-unit-tester.py
+++ b/Trigger/TrigValidation/TrigValTools/bin/trigvalsteering-unit-tester.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python
 #
-# Copyright (C) 2002-2019 CERN for the benefit of the ATLAS collaboration
+# Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
 #
 
 import sys
@@ -27,7 +27,7 @@ def grep_errors(filename):
     lines = []
     with open(filename) as f:
         lines = re.findall(error_pattern, f.read(), re.MULTILINE)
-    return filter(filter_fn, lines)
+    return list(filter(filter_fn, lines))
 
 
 def main():