diff --git a/live-build/functions b/live-build/functions
index 484e5046..ac4912f5 100644
--- a/live-build/functions
+++ b/live-build/functions
@@ -461,7 +461,7 @@ snap_prepare() {
     local CHROOT_ROOT=$1
     # Optional. If set, should be a colon-separated string of brand:model to be
     # used for the image's model assertion
-    local CUSTOM_BRAND_MODEL=$2
+    local CUSTOM_BRAND_MODEL=${2:-generic:generic-classic}
 
     snap_prepare_assertions "$CHROOT_ROOT" "$CUSTOM_BRAND_MODEL"