diff --git a/django/forms/widgets.py b/django/forms/widgets.py
index dd5868f..891fe34 100644
--- a/django/forms/widgets.py
+++ b/django/forms/widgets.py
@@ -482,6 +482,7 @@ class CheckboxInput(Widget):
         if value not in ('', True, False, None):
             # Only add the 'value' attribute if a value is non-empty.
             final_attrs['value'] = force_unicode(value)
+        final_attrs['class'] = final_attrs.get('class', '') + ' checkbox'
         return mark_safe(u'<input%s />' % flatatt(final_attrs))
 
     def value_from_datadict(self, data, files, name):
@@ -630,6 +631,7 @@ class RadioInput(StrAndUnicode):
         final_attrs = dict(self.attrs, type='radio', name=self.name, value=self.choice_value)
         if self.is_checked():
             final_attrs['checked'] = 'checked'
+        final_attrs['class'] = final_attrs.get('class', '') + ' radio'
         return mark_safe(u'<input%s />' % flatatt(final_attrs))
 
 class RadioFieldRenderer(StrAndUnicode):