diff --git a/http-cookie.gemspec b/http-cookie.gemspec
index fc5c2f0..0d6f799 100644
--- a/http-cookie.gemspec
+++ b/http-cookie.gemspec
@@ -29,7 +29,7 @@ Gem::Specification.new do |gem|
   gem.add_development_dependency("bundler", [">= 1.2.0"])
   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("rdoc", RUBY_VERSION > "1.9" ? "> 2.4.2" : "~> 2.4.2")
   gem.add_development_dependency("simplecov", [">= 0"])
   gem.add_development_dependency("json", ["< 2"]) if RUBY_VERSION < "2.0"
 end