diff --git a/lib/repubmark.rb b/lib/repubmark.rb
index f9841d2..7efab65 100644
--- a/lib/repubmark.rb
+++ b/lib/repubmark.rb
@@ -9,6 +9,7 @@ require 'uri'
 require 'yaml'
 
 require 'addressable'
+require 'ast'
 require 'bibtex'
 
 require_relative 'repubmark/highlight'
diff --git a/repubmark.gemspec b/repubmark.gemspec
index 72f1c69..ab22895 100644
--- a/repubmark.gemspec
+++ b/repubmark.gemspec
@@ -47,6 +47,7 @@ Gem::Specification.new do |spec|
   spec.executables = spec.files.grep(%r{\Aexe/}) { |f| File.basename f }
 
   spec.add_dependency 'addressable', '~> 2.8'
+  spec.add_dependency 'ast',         '~> 2.4'
   spec.add_dependency 'bibtex-ruby', '~> 6.1'
   spec.add_dependency 'i18n',        '~> 1.14'
 end