diff --git a/ckan/templates/macros/form.html b/ckan/templates/macros/form.html
index fe13fc43df6..88136a24491 100644
--- a/ckan/templates/macros/form.html
+++ b/ckan/templates/macros/form.html
@@ -340,7 +340,7 @@
     {% form.hidden(fields=c.fields, except=[('topic', 'xyz')]) %}
     {% form.hidden(fields=c.fields, except_names=['time_min', 'time_max']) %}
 #}
-{% macro hidden_list(fields, except_names=[], except=[]) %}
+{% macro hidden_list(fields, except_names=None, except=None) %}
   {% set except_names = except_names or [] %}
   {% set except = except or [] %}