diff --git a/ssh_router.sh b/ssh_router.sh
index dc9f1ff..458d11a 100644
--- a/ssh_router.sh
+++ b/ssh_router.sh
@@ -82,7 +82,7 @@ ensure_image
 
 # ─────────────────────────────────────────────
 # Disallow file transfers
-case "$SSH_ORIGINAL_COMMAND" in
+case "${SSH_ORIGINAL_COMMAND:-}" in
 *scp* | *sftp* | *rsync* | *tar*)
   log ERROR "File transfers are disabled"
   exit 1