diff --git a/lib/optparse/optparse.gemspec b/lib/optparse/optparse.gemspec
index ae6596678c..a4287ddeee 100644
--- a/lib/optparse/optparse.gemspec
+++ b/lib/optparse/optparse.gemspec
@@ -23,6 +23,7 @@ Gem::Specification.new do |spec|
   spec.metadata["source_code_uri"] = spec.homepage
 
   spec.files         = Dir["{doc,lib,misc}/**/*"] + %w[README.md ChangeLog COPYING]
+  spec.rdoc_options  = ["--main=README.md", "--op=rdoc", "--page-dir=doc"]
   spec.bindir        = "exe"
   spec.executables   = []
   spec.require_paths = ["lib"]