Index: django/forms/widgets.py
===================================================================
--- django/forms/widgets.py	(revision 8129)
+++ django/forms/widgets.py	(working copy)
@@ -359,6 +359,8 @@
                 escape(option_value), selected_html,
                 conditional_escape(force_unicode(option_label)))
         # Normalize to strings.
+        if not hasattr(selected_choices, '__iter__'):
+            selected_choices = [selected_choices]
         selected_choices = set([force_unicode(v) for v in selected_choices])
         output = []
         for option_value, option_label in chain(self.choices, choices):