diff --git a/lib/sinatra/main.rb b/lib/sinatra/main.rb
index fc6ac70d..48af1adc 100644
--- a/lib/sinatra/main.rb
+++ b/lib/sinatra/main.rb
@@ -13,11 +13,11 @@ module Sinatra
     if run? && ARGV.any?
       require 'optparse'
       OptionParser.new { |op|
-        op.on('-x')        {       set :lock, true }
-        op.on('-e env')    { |val| set :environment, val.to_sym }
-        op.on('-s server') { |val| set :server, val }
-        op.on('-p port')   { |val| set :port, Integer(val) }
-        op.on('-o addr')   { |val| set :bind, val }
+        op.on('-p port',   'set the port (default is 4567)')                { |val| set :port, Integer(val) }
+        op.on('-o addr',   'set the host (default is 0.0.0.0)')             { |val| set :bind, val }
+        op.on('-e env',    'set the environment (default is development)')  { |val| set :environment, val.to_sym }
+        op.on('-s server', 'specify rack server/handler (default is thin)') { |val| set :server, val }
+        op.on('-x',        'turn on the mutex lock (default is off)')       {       set :lock, true }
       }.parse!(ARGV.dup)
     end
   end