diff --git a/gollum.gemspec b/gollum.gemspec
index 8ecb721e..ee519e28 100644
--- a/gollum.gemspec
+++ b/gollum.gemspec
@@ -20,6 +20,7 @@ Gem::Specification.new do |s|
   s.rdoc_options = ['--charset=UTF-8']
   s.extra_rdoc_files = %w[README.md LICENSE]
 
+  s.add_dependency 'rdoc', '~> 6'
   s.add_dependency 'gollum-lib', '~> 5.1'
   s.add_dependency 'kramdown', '~> 2.3'
   s.add_dependency 'kramdown-parser-gfm', '~> 1.1.0'