diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index c0253f86b..779f050e4 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -162,6 +162,10 @@ class Field(object):
         attrs = {}
         if 'id' not in self.widget.attrs:
             attrs['id'] = self._name
+        if not 'class' in self.widget.attrs:
+            attrs['class'] = 'form-control'
+        elif attrs['class'].find('form-control') == -1:
+            attrs['class'] += ' form-control'
 
         return self.widget.render(self._name, self._value, attrs=attrs)