diff --git a/lib/un.rb b/lib/un.rb
index 4a15a37394..628260a7fa 100644
--- a/lib/un.rb
+++ b/lib/un.rb
@@ -22,7 +22,7 @@
 #   ruby -run -e touch -- [OPTION] FILE
 #   ruby -run -e wait_writable -- [OPTION] FILE
 #   ruby -run -e mkmf -- [OPTION] EXTNAME [OPTION]
-#   ruby -run -e httpd -- [OPTION] DocumentRoot
+#   ruby -run -e httpd -- [OPTION] [DocumentRoot]
 #   ruby -run -e help [COMMAND]
 
 require "fileutils"
@@ -304,7 +304,7 @@ end
 ##
 # Run WEBrick HTTP server.
 #
-#   ruby -run -e httpd -- [OPTION] DocumentRoot
+#   ruby -run -e httpd -- [OPTION] [DocumentRoot]
 #
 #   --bind-address=ADDR         address to bind
 #   --port=NUM                  listening port number