diff --git a/README.md b/README.md
index bcdde03..5c947c2 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,7 @@ Base on Ubuntu, using Docker to construct your Apt mirror HTTP server
 
 ## Usage
 ```
-docker run -d -P port_number:80 -v /path/your_mirror.list:/etc/apt/ seterrychen/apt-mirror-http-server
+docker run -d -p port_number:80 -v /path/your_mirror.list:/etc/apt/ seterrychen/apt-mirror-http-server
 ```
 
 If you don't provide mirror.list file, the program will use default setting.