diff --git a/django/contrib/formtools/preview.py b/django/contrib/formtools/preview.py
index 351d991762..dcb58e85d8 100644
--- a/django/contrib/formtools/preview.py
+++ b/django/contrib/formtools/preview.py
@@ -83,7 +83,7 @@ class FormPreview(object):
         """
         while 1:
             try:
-                f = self.form.fields[name]
+                f = self.form.base_fields[name]
             except KeyError:
                 break # This field name isn't being used by the form.
             name += '_'