diff --git a/asset_sync.gemspec b/asset_sync.gemspec
index b815dc07..dc9907e8 100644
--- a/asset_sync.gemspec
+++ b/asset_sync.gemspec
@@ -21,6 +21,7 @@ Gem::Specification.new do |s|
   s.add_dependency('fog', ">= 1.8.0")
   s.add_dependency('unf')
   s.add_dependency('activemodel')
+  s.add_dependency('mime-types')
 
   s.add_development_dependency "rspec"
   s.add_development_dependency "bundler"