1 files changed, 21 insertions, 2 deletions
diff --git a/guides/rails_guides.rb b/guides/rails_guides.rb
index ab890f202c..9d488a8a15 100644
--- a/guides/rails_guides.rb
+++ b/guides/rails_guides.rb
@@ -5,7 +5,7 @@ $:.unshift pwd
 def bundler?
   # Note that rake sets the cwd to the one that contains the Rakefile
   # being executed.
-  File.exists?('Gemfile')
+  File.exist?('Gemfile')
 end
 
 begin
@@ -22,7 +22,7 @@ end
 
 begin
   require 'redcarpet'
-rescue Gem::LoadError
+rescue LoadError
   # This can happen if doc:guides is executed in an application.
   $stderr.puts('Generating guides requires Redcarpet 2.1.1+.')
   $stderr.puts(<<ERROR) if bundler?
@@ -39,6 +39,25 @@ ERROR
   exit 1
 end
 
+begin
+  require 'nokogiri'
+rescue LoadError
+  # This can happen if doc:guides is executed in an application.
+  $stderr.puts('Generating guides requires Nokogiri.')
+  $stderr.puts(<<ERROR) if bundler?
+Please add
+
+  gem 'nokogiri'
+
+to the Gemfile, run
+
+  bundle install
+
+and try again.
+ERROR
+  exit 1
+end
+
 require 'rails_guides/markdown'
 require "rails_guides/generator"
 RailsGuides::Generator.new.generate