diff --git a/lib/net/net-smtp.gemspec b/lib/net/net-smtp.gemspec
index cf1c3b7815..e281b05bf6 100644
--- a/lib/net/net-smtp.gemspec
+++ b/lib/net/net-smtp.gemspec
@@ -30,4 +30,6 @@ Gem::Specification.new do |spec|
   spec.require_paths = ["lib"]
 
   spec.add_dependency "net-protocol"
+  # spec.add_dependency "digest"
+  spec.add_dependency "timeout"
 end