diff --git a/tool/rdoc-srcdir b/tool/rdoc-srcdir
index 304deb67ce..03e5171650 100755
--- a/tool/rdoc-srcdir
+++ b/tool/rdoc-srcdir
@@ -1,5 +1,6 @@
-#!ruby
+#!ruby -W0
 
+$:.unshift(File.expand_path("../lib", __dir__))
 require 'rdoc/rdoc'
 
 # Make only the output directory relative to the invoked directory.