diff --git a/seafile_sync/Dockerfile b/seafile_sync/Dockerfile
index 6950814..c772be4 100644
--- a/seafile_sync/Dockerfile
+++ b/seafile_sync/Dockerfile
@@ -1,2 +1,4 @@
 # https://gitlab.com/flwgns-docker/seafile-client/
+ARG \
+    SEAF_SERVER_URL
 FROM flowgunso/seafile-client:latest