diff --git a/compose.yml b/compose.yml
index de1abd6b..e7926abd 100644
--- a/compose.yml
+++ b/compose.yml
@@ -3,7 +3,7 @@ services:
     image: qemux/qemu
     container_name: qemu
     environment:
-      BOOT: "alpine"
+      BOOT: ${BOOT-alpine}
     devices:
       - /dev/kvm
       - /dev/net/tun