diff --git a/fog.gemspec b/fog.gemspec
index 66dcbd392..de86d1698 100644
--- a/fog.gemspec
+++ b/fog.gemspec
@@ -75,6 +75,7 @@ Gem::Specification.new do |s|
 
   s.add_development_dependency("docker-api", ">= 1.13.6")
   s.add_development_dependency("fission")
+  s.add_development_dependency("mime-types")
   s.add_development_dependency("minitest")
   s.add_development_dependency("minitest-stub-const")
   s.add_development_dependency("opennebula")