uninformative error message when using 'markdown' helper without bluecloth gem

If you happen to use the markdown helper, like so:

<%= markdown(post.body) %>

You get a pretty uninformative error message:

ActionView::Template::Error (uninitialized constant ActionView::Helpers::TextHelper::BlueCloth) on line #4 of /Users/technicalpickles/code/scratch/rails-3-blog/app/views/posts/_post.html.erb:
1: <h2><%= link_to post, post %></h2>
2: 
3: <div id="<%= dom_id(post) %>" class="<%= dom_class(post) %>">
4:   <div class="body"><%= markdown(post.body) %></div>
5: 
6:   <ul class="actions">
7:     <li><%= 'Not' unless post.published? %> Published</li>

    app/views/posts/_post.html.erb:4:in `_render_template_887285710_17704920_230336'
    app/views/posts/show.html.erb:1:in `_render_template__976704918_17747910_0'
    app/controllers/posts_controller.rb:18:in `show'

Fortunately, I'm familiar enough with markdown and bluecloth to know it needs the bluecloth gem, so I'd add this to Gemfile:

gem 'bluecloth'

This doesn't really fix the problem. I double checked that BlueCloth is defined by bluecloth.rb, and it is.

The only way I was able to get it to work was:

<% require 'bluecloth' %>
<%= markdown(post.body) %>

I would have guessed this would have happened by adding it to Gemfile, or at latest, inside the markdown helper.