diff --git a/src/kemal.cr b/src/kemal.cr
index 65954ca..7029a80 100644
--- a/src/kemal.cr
+++ b/src/kemal.cr
@@ -5,11 +5,14 @@ require "./kemal/middleware/*"
 
 module Kemal
   # The command to run a `Kemal` application.
-  def self.run
+  # The port can be given to `#run` but is optionnal.
+  # If not given Kemal will use the default config port (`Kemal::Config#port`)
+  def self.run(port = nil)
     Kemal::CLI.new
     config = Kemal.config
     config.setup
     config.add_handler Kemal::RouteHandler::INSTANCE
+    config.port = port if port
 
     config.server = HTTP::Server.new(config.host_binding, config.port, config.handlers)
     {% if ! flag?(:without_openssl) %}