diff --git a/jekyll.gemspec b/jekyll.gemspec
index 5754e2e7..53882996 100644
--- a/jekyll.gemspec
+++ b/jekyll.gemspec
@@ -46,6 +46,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency('simplecov', "~> 0.7")
   s.add_development_dependency('simplecov-gem-adapter', "~> 1.0.1")
   s.add_development_dependency('coveralls', "~> 0.7.0")
+  s.add_development_dependency('mime-types', "~> 1.5")
   s.add_development_dependency('activesupport', '~> 3.2.13')
   s.add_development_dependency('jekyll_test_plugin')