diff --git a/gestioncof/widgets.py b/gestioncof/widgets.py
index 49125896..9206d441 100644
--- a/gestioncof/widgets.py
+++ b/gestioncof/widgets.py
@@ -11,7 +11,7 @@ class TriStateCheckbox(Widget):
         # more than once.
         self.choices = list(choices)
 
-    def render(self, name, value, attrs=None, choices=()):
+    def render(self, name, value, attrs=None, choices=(), renderer=None):
         if value is None:
             value = "none"
         attrs["value"] = value