 <p>What version of Simple_form are you using? How did you integrate bootstrap?</p> <p>Presuming you used simple_form's wiki to integrate with twitter/bootstrap then please verify:</p> <ol> <li>lib/simple_form/contained_input_component.rb is being loaded and is implemented as-is</li> <li>config/initializers/simple_form.rb is calling the above library</li> <li>there is only one simple_form.rb in config/initializers and config/production</li> </ol> <p>If all of the above is in order, please update the question with your view code.</p>