diff --git a/docker/classic/Dockerfile b/docker/classic/Dockerfile
index 33ce58ed..f9b91d6a 100644
--- a/docker/classic/Dockerfile
+++ b/docker/classic/Dockerfile
@@ -1,3 +1,5 @@
+ARG SHAIRPORT_SYNC_BRANCH=.
+
 FROM alpine:3.17 AS builder
 
 # Classic (aka AirPlay 1) Build