Index: django/forms/fields.py
===================================================================
--- django/forms/fields.py	(revision 11679)
+++ django/forms/fields.py	(working copy)
@@ -454,7 +454,7 @@
         super(FileField, self).__init__(*args, **kwargs)
 
     def clean(self, data, initial=None):
-        super(FileField, self).clean(initial or data)
+        data = super(FileField, self).clean(data or initial)
         if not self.required and data in EMPTY_VALUES:
             return None
         elif not data and initial: