Index: django/newforms/models.py
===================================================================
--- django/newforms/models.py	(revision 4525)
+++ django/newforms/models.py	(working copy)
@@ -29,7 +29,10 @@
     opts = instance.__class__._meta
     if form.errors:
         raise ValueError("The %s could not be changed because the data didn't validate." % opts.object_name)
-    clean_data = form.clean_data
+    clean_data = dict([
+        (k, isinstance(v, unicode) and v.encode(settings.DEFAULT_CHARSET) or v)
+        for k, v in form.clean_data.items()
+    ])
     for f in opts.fields:
         if isinstance(f, models.AutoField):
             continue