diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index 3fef619de6..db3732e072 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -1493,6 +1493,16 @@ strio_set_encoding(int argc, VALUE *argv, VALUE self)
 
 /*
  * Pseudo I/O on String object.
+ *
+ * Commonly used to simulate `$stdio` or `$stderr`
+ *
+ * === Examples
+ *
+ *   require 'stringio'
+ *
+ *   io = StringIO.new
+ *   io.puts "Hello World"
+ *   io.string #=> "Hello World"
  */
 void
 Init_stringio()