diff --git a/README.md b/README.md
index 89429df..d7ba9be 100644
--- a/README.md
+++ b/README.md
@@ -17,7 +17,7 @@ docker pull ghcr.io/wfg/wireguard
 
 To build it yourself, run
 ```
-docker build -t ghcr.io/wfg/wireguard https://github.com/wfg/docker-wireguard.git#main:build
+docker build -t ghcr.io/wfg/wireguard --build-arg WGT_GIT_REF=master https://github.com/wfg/docker-wireguard.git#main:build
 ```
 
 ### Creating and running a container