nesting comments resources in posts resources - ruby-on-rails-4

Question

I'm doing the RoR tutorial on rubyonrails.org and have been doing fine up until adding comments to posts.
When I click through to 'show' a post, I get the following error:
ActionController::UrlGenerationError in Posts#show
No route matches {:action=>"index", :controller=>"comments", :id=>"1", :format=>nil} missing required keys: [:post_id]
I have a show method for posts_controller.rb (see below), and, unless there's a typo on the rails guide (likely, since there are others in other spots), I think there's something going on with my routes.rb.
It says the error occurs around line 25 of /show.html.erb.
Title:
<%= #post.title %>
<p>
<strong>Text:</strong>
<%= #post.text %>
</p>
<h2>Comments</h2>
<% #post.comments.each do |comment| %>
<p>
<strong>Commenter:</strong>
<%= comment.commenter %>
</p>
<p>
<strong>Comment:</strong>
<%= comment.body %>
</p>
<% end %>
<h2>Add a comment:</h2>
<%= form_for([:post, #post.comments.build]) do |f| %>
<p>
<%= f.label :commenter %><br />
<%= f.text_field :commenter %>
</p>
<p>
<%= f.label :body %><br />
<%= f.text_area :body %>
</p>
<p>
<%= f.submit %>
</p>
<% end %>
<%= link_to 'Back', posts_path %>
<%= link_to 'Edit', edit_post_path(#post) %>
/posts_controller.rb
class PostsController < ApplicationController
def new
#post = Post.new
end
def index
#post = Post.all
end
def show
#post = Post.find(params[:id])
end
def create
#post = Post.new(params[:post].permit(:title, :text))
if #post.save
redirect_to #post
else
render 'new'
end
def edit
#post = Post.find(params[:id])
end
end
def update
#post = Post.find(params[:id])
if #post.update(params[:post].permit(:title, :text))
redirect_to #post
else
render 'edit'
end
end
def destroy
#post = Post.find(params[:id])
#post.destroy
redirect_to posts_path
end
private
def post_params
params.require(:post).permit(:title, :text)
end
end
routes.rb
Myapp::Application.routes.draw do
resources :posts do
resources :comments
end
root "welcome#index"
end
I think the error has something to do with my routes.rb file, but I can't figure out exactly what. Am I nesting my routes for the comments incorrectly?