diff --git a/select2/widgets.py b/select2/widgets.py
index 15ea20f..a4afd65 100644
--- a/select2/widgets.py
+++ b/select2/widgets.py
@@ -68,12 +68,12 @@ def __init__(self, attrs=None, choices=(), js_options=None, *args, **kwargs):
 
         self.attrs.update({
             'data-placeholder': kwargs.pop('overlay', None),
-            'class': combine_css_classes(attrs.get('class', ''), self.default_class),
             'data-sortable': json.dumps(self.sortable),
         })
-
         self.attrs.update(attrs)
-        self.choices = iter(choices)
+        self.attrs['class'] = combine_css_classes(attrs.get('class', ''),
+                                                  self.default_class)
+        self.choices = choices
 
     def reverse(self, lookup_view):
         opts = getattr(self, 'model', self.field.model)._meta