diff --git a/cybertools/composer/schema/grid/field.py b/cybertools/composer/schema/grid/field.py
index f6c4a17..62ee6f7 100644
--- a/cybertools/composer/schema/grid/field.py
+++ b/cybertools/composer/schema/grid/field.py
@@ -88,12 +88,12 @@ class GridFieldInstance(ListFieldInstance):
         headers = [fi.context.title for fi in self.columnFieldInstances]
         rows = []
         value = value or []
-        cardinality = getattr(self.context, 'cardinality', None)
+        cardinality = getattr(self.context, 'cardinality', None) or 0
         for item in value:
             rows.append([fi.display(item.get(fi.name))
                             for fi in self.columnFieldInstances])
         if cardinality > len(value):
-            for item in range(len(value), self.context.cardinality):
+            for item in range(len(value), cardinality):
                 rows.append([fi.display(fi.default) 
                                 for fi in self.columnFieldInstances])
         empty = not rows or (len(rows) == 1 and not [v for v in rows[0] if v])