diff --git a/http-cookie.gemspec b/http-cookie.gemspec
index b655d86..02cdfd0 100644
--- a/http-cookie.gemspec
+++ b/http-cookie.gemspec
@@ -27,7 +27,7 @@ Gem::Specification.new do |gem|
   gem.add_runtime_dependency("domain_name", ["~> 0.5"])
   gem.add_development_dependency("sqlite3", ["~> 1.3.3"]) unless defined?(JRUBY_VERSION)
   gem.add_development_dependency("bundler", [">= 1.2.0"])
-  gem.add_development_dependency("test-unit", [">= 2.4.3"])
+  gem.add_development_dependency("test-unit", [">= 2.4.3", *("< 3" if RUBY_VERSION < "1.9")])
   gem.add_development_dependency("rake", [">= 0.9.2.2", *("< 11" if RUBY_VERSION < "1.9")])
   gem.add_development_dependency("rdoc", ["> 2.4.2"])
   gem.add_development_dependency("simplecov", [">= 0"])